use principaluri instead of userid, allowing to add delegates for rooms and things

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup add owner_id and proxy_id as db index, since we use it for querying

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup don't add ACL for each individual proxy, just use calendar-proxy groups

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup allow delegation of resources / rooms

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup fix addIndex call in migration

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup fix remaining constructor calls of Principal

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

!fixup minor fixes and unit tests

Signed-off-by: Georg Ehrke <developer@georgehrke.com>