changed: allow libname for hidden extension points

needed for repository add-ons
changed: allow calling non-plugin extension points as plugins
added: support python based add-on installers

these are called as a vfs plugin with parameters.
reindent
Merge pull request #2816 from cptspiff/python_installers

Python based add-on installers
Use the new value of avi mime type in test
Clear file from cache in CDirectory::Remove()
Only append filename to strDestFile when not a folder
Change to use IsWindowsVersionAtleast(..)
cosmetics: get rid of int64_t to int warning
Restructure CFileOperationJob::DoProcess(..)
[UPNP/JSONRPC] Allow usage of path that are inside sources + add source
setting allowSharing

Continuation of 1220d8c4a9
Add a source flag allowsharing defaulting to true to allow or disallow
access to a source from UPNP/WebServer

The checks are now available as a function in FileUtils and common to UPNP and JSON
Also make the check correctly works in JSON as current implementation have flow allowing browsing any directory with Files.GetDirectory.
settings: introduce ISettingsHandler::OnSettingsUnloaded()
advancedsettings: fix multiple initialization overwriting app parameters like "-fs" etc
renderer: we must give renderer a head start in non fullscreen

If we don't the next frame will be late right of the bat and
we end up dropping it.
renderer: clean up CRetakeLock to avoid deadlocks

If we Leave() and Enter() the order of locks are reversed again.
Merge pull request #2764 from Tolriq/upnp_checksource

[UPNP/JSONRPC] add source setting allowSharing to secure source access from UPNP/WebServer
Merge pull request #2824 from Montellese/settings_unloading

settings: fix handling of settings unloading
Remove DownloadQueue & DownloadQueueManager
Remove broken usage of CSettingsCategory & CSettings