[Doc] 2.2 user manual updates

Documentation draft to introduce notifications.

The assert was there to make sure that this case wasn't happening
to eventually be properly tested. Remove the assert for now but this
codepath should eventually be unit tested using this specific situation.

Also added a screenshot.

Since the windows implementation first does cache lookups using the
path string, directories need to be passed identically as through
RETRIEVE_FILE_STATUS.

Change the convention to never have a trailing slash for directories
in the protocol. This allows the convention to be applied without
having to access the disk (since we'd need to know if the path is
represented by a directory) and also matches the convention of the
rest of the sync engine. Individual file manager plugins are then
responsible of handling pushed paths as not ending with a trailing
slash.

This also:
- Moves the trailing slash removal logic from the SyncFileStatusTracker
  to the SocketApi class
- Remove the unneeded QString::normalized call in fileStatus, since
  this should already be done by the FolderWatcher and plugins

Make sure that the name of the _export.h file is the same no matter the plugin

Viel hilft viel ;-)

Since the statuses are cached and that we can't invalidate the cache,
sending NOP would need to be overwritten by the default OK status
once the client successfully connected. But instead of remembering
which files we NOPed, rather wait until we are ready to sync before
sending the REGISTER_PATH message to the socket API client. It will
also prevent the client from sending unnecessary RETRIEVE_FILE_STATUS
requests.

Also remove AccountState::canSync, since it does the same as
isConnected and syncing is not an account responsibility.

Having an overload as a private function in the same class makes the
code harder to follow. Rename the private fileStatus to syncFileItemStatus.

Go through fileStatus like other cases to make sure that all use
cases go through the same code path. This also makes sure to use
lookupProblem which will use lower_bound which is more efficient
for larger sets of sync problems.

This also fixes the issue with lookupProblem that prevented it to
properly match an empty pathToMatch, caused by the fact that the
problem map contains relative paths not starting with a slash.

Make sure that we push the new status when the status of the SyncEngine
changed. SyncEngine::started comes a bit late, only when the propagation
starts, although it's better in this case since child folders will
only switch to Sync in aboutToPropagate.

Also fix an issue with SyncEngine::findSyncItem when using an empty
fileName; this would match and return the wrong item, even though
not currently happening with the code since fileStatus won't call
it with an empty fileName anymore.

As before, we rely on metadata-update SyncFileItem entries for parent
directories to notify us that a directory contains files to propagate,
and to know when all children were propagated through its itemCompleted
signal.

Those metadata SyncFileItems however have a None direction and we need
to add a explicit directory check to show them as Sync.
This fix also handles new files as well as existing ones, so no need
to keep a separate logic for new files.

* Fix nautilus and nemo plugin branding strings.

Fix for owncloud/enterprise#1314

* nautilus plugin: Add a comment why the line needs to stay unchanged.

propagatedownload.cpp:712:35: error: 'seenLockedFile' is a protected member of 'OCC::OwncloudPropagator'

Signals are protected in Qt4 but public in Qt5, mark the class accessing it
as friend when compiling with Qt4

Addresses #3411

Do the visual stuff from designer.
The previous code that was ment to change the color in red did not work
and changed it to gray instead.
Also I don't see why there should be a frame.

Issue #4773

When a conflict-rename or a temporary-rename fails, notify the
LockWatcher. It'll regularly check whether the file has become
accesible again. When it has, another sync is triggered.

owncloud/enterprise#1288

Fixed #4740

When searching for sharees we should display a loading spinner.