renderer: replace render buffer indices with queues
renderer: simplify code by always maintaining one front buffer
renderer: remove now pointless GetNext(Decode/Render) function
renderer: name present buffer structure to be able to reference it
renderer: store bypass format in rendermanager instead

The present method will be overwritten on each flippage
renderer: drop copies of variables, use queue data directly
renderer: grab presentlock in AddVideoPicture
[Linux] Read OS information from /etc/os-release
Most modern Linux distributions use the /etc/os-release
file for operating system information.
This patch will try to read the PRETTY_NAME variable from
/etc/os-release to identify the Linux distribution.

If /etc/os-release doesn't exist, the code will still fall back
to lsb_release or the distro-specific release files.

http://www.freedesktop.org/software/systemd/man/os-release.html
http://0pointer.de/blog/projects/os-release.html
removed: BackGroundInfo Loader multithreading (no longer needed)
changed: Split background info loading into a 2 stages

This allows us to first perform loading of cached (fast) stuff and after that load the lookup (slow) stuff (partially fixes #14071)
Merge pull request #2900 from mus65/os-release

[Linux] Read OS information from /etc/os-release
Merge pull request #2811 from FernetMenta/erenderbuf

renderer: replace ring buffer logic with queues for free, queued, and discarded buffers
Remove extraneous empty-string check (URIUtils::IsInternetStream() and CFile::Exists() both handle empty strings)
Don't show "Add to Favorites" context button for "Get More..." add-on links
changed: Renamed m_database to m_video/m_musicDatabase for clarity
changed: Use a member variable for the texture database

This speeds up thumb loading considerably. This also gets rid of the Initialize/Deinitialize ThumbLoader functions
fixed: Music thumb loading for files view was slow

This was caused by the fact that we never checked for cached images for music items
fixed: Thumb/flag extractions were never stored when used outside the bg infoloader

Also factored out some (obsolote?) code as a bonus
Merge pull request #2890 from arnova/thumb_loader_refactor

Thumb loader refactor
[rbp/omxplayer] Explicitly set number of output channels on audio_mixer