Those won't be used by the docs app, but this way they will be
available in release version of the docs app, and people can use
those files as input to JSDuck.

Added --videos option.

Created simple Videos class for parsing the JSON.

--guides option now must point to a JSON file.
--guides-order option removed.

The file is read in, parsed, and the guides listed in it are
copied to output_dir/guides + the usual Markdown conversion.

Additionally the list of guides is written to tree.js as Docs.guides.
So no separate .js file for guides is needed.

The guides HTML is no more written inside index.html

First off just placing guides.js and videos.js to SDK/guides/
and including them in index.html

Something relies on this store... didn't really figure out what.
For example opening a video caused an exception.

Now that all stores use the same Model structure, we can move
it up to ThumbList class, but instead of explicitly creating a
store, we simply use this.data.

Now instead of defining the whole template when instanciating ThumbList,
only defining the part that differs - the itemTpl.

The JSON for all these will have records with fields:

- id
- title
- items

For two classes these were simply unused. For the third class they
could be more compactly expressed inline.

e.g. when last tab was guide, activate guides index.

Given that guides are all expanded, videos should behave the same.
Or the other way around, but I feel all-expanded is better, as
it allows you to scroll through all items easily without being
forced to click expand-expand-expand...

Makes more sense now that we have different types of trees.

- Removed needless required classes from Viewport.
- videos/guides/examples Index classes now require their own List.
- Not using Ext.create('Ext.XTemplate') at class definition time.

- Add doc-comments to all classes.
- Add missing semicolons, remove trailing commas.
- Use Ext.Array.forEach instead of strange for-loop.
- Use === instead of ==.
- Rmove some commented-out code.
- Several other code style improvements.

It's now done by Guides class method #to_tree.