[rbp/omxplayer] Merge with current dvdplayer

To make spotting differences between omxplayer and dvdplayer easier in the future,
this is a pretty slavish copy, including dvdplayer's whitespace and header file includes.
You now get a pretty clean diff between dvdplayer.cpp/dvdplayer.h and omxplayer.cpp/omxplayer.h
Also show audio language in the KAI toast when cycling through audio tracks with ACTION_AUDIO_NEXT_LANGUAGE.
Currently only codec/channels are shown.
Merge pull request #2798 from popcornmix/merge_dvdplayer

[rbp/omxplayer] Merge with current dvdplayer
Merge pull request #2781 from mikkle/ShowAudioLanguageInToast

[GUI/Player] Proper audio track lang-name string for kai toast
process border image after base image to ensure it's positioned correctly the first frame the base image is available
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