Do not generate any networking projects for Angle. Angle is just for testing GLES and does not need networking.

Fixes #2592
Merge pull request #2603 from danzel/no-angle-net

Do not generate any networking projects for Angle.
Added custom IEqualityComparer to SpriteFont glyph dictionary.
Replaced internal _texture access.
Removed _characters in favor of auto-property.
Simplified logic around missing glyphs.
Removed always true if statement.
Merge pull request #2604 from SickheadGames/fonts

SpriteFont Optimizations Pt. 1
Don't stop the Stopwatch until we are ready to start the run loop. Previously we'd be accumulating update time while the game loaded, which would lead to _maxElapsedTime worth of updates before the first draw call was made.
Redo the IsRunningSlowly calculation to use a method that closer resembles XNA behaviour. We now count how many lost frames we've had and use that as the trigger.

Fixes #2595
Merge pull request #2607 from danzel/isrunningslowly

Redo the IsRunningSlowly calculation
Merge pull request #2606 from danzel/gamestart-update-spam

Fix burst of Game.Update calls at the start of the game
flibit regrets not doing his homework on XACT back in October
I hate this timer and its entire family
Fix redundant Stop on delayed Instance
Merge back from develop
Merge branch 'flibitijibibo-monogame-sdl2' into monogame-sdl2