Many mostly graphics related changes

[paulwedeck]

I reduced the number of shader to three:

• normal unified shader (now including texes and colors functionality) (GL(ES) 2.0)
• unified-array to bundle multiple drawings of a single quad at multiple locations/colors (GLES 3.0 /GL_EXT_draw_instanced
• unified-multi to bundle drawing of different objects at different locations (GLES32/ GL_EXT_geometry_shader4 &GL_ARB_uniform_buffer_object)

There no longer is any pre gl2 render path because there are barly any remaining users:

• for desktop gl (https://feedback.wildfiregames.com/report/opengl/feature/GL_VERSION)
• for android (https://developer.android.com/about/dashboards/index.html#OpenGL)

I rewrote the FogOfWar algorithm to better fit the Backgrounds needs and to respect to current game speed/pause status.

GeometryHandles are no replaced by *DrawHandles. Most Textures and Geometries are bundled together in ManagedHandles hold by GLDrawContext that only create a single buffer and texture instead of one per SingleImage. Only parts of ManagedHandles can be used to draw via the unified-multi shader.

[andreas-eberle]

Wow, this looks massive. I'll need some time to check this all out. Thanks already for your work!

[paulwedeck]

419b2e2 fixes #769 for some characters (only that that I could extract from the labels_* files)