3.5.0 Release

This is a stable 3.5.0 release. The contents of this update are listed in Changes.txt as usual.

People who were working on this release:
@AlanDrake
@ivan-mogilko
@kmar (new pathfinding)
@mgambrell (better threaded audio support and bug fixes)
@monkey0506 (steam/gog plugin stubs)
@morganwillcock
@persn (Editor's Color Themes)
@rofl0r (bug fixes)
@scottchiefbaker (fixes to building on some Linux systems)
@sonneveld
@tobihan (fixes to building on some Linux systems)
@toojays (OpenGL support on Linux)
@tzachshabtay (new navigation bar for the Room Editor)

NOTES:
The iOS port was not properly updated, and may not compile without few manual changes. This is a known issue and hopefully will be resolved in following minor updates (e.g. 3.5.1). The main reason is that it still relies on older Allegro version and requires old hacks to work.