window.cpp: small cleanups

Constify static numbers
'unsigned char' -> 'uint8_t'
etc.h: Constify methods
gl-util.h: Add GL ID != operator and TEXFBO::clear

TEXFBO::clear resets the struct into its state right
after creation, nulling all IDs inside so they're invaid.
quad.h: Cleanup static functions to use templated Vertex parameter

Collapses all the different Vertex/SVertex/CVertex variants
into one generic one per function.
quadarray.h: Use size_t for everything (quad) count related
SharedState: Constify most getter methods
DisposeWatch: Make private and constify members
Use correct default resolution for RGSS2/3 (544x416)
Tone: Add 'valueChanged' signal
Add internal 'KeepDestAlpha' BlendType (for use in WindowVX)
Implement RGSS2 Window class (WindowVX)
Tilemap: Fix typo
Tilemap: Make Autotiles con/destructor private
Implement RGSS2 Tilemap class (TilemapVX)
mkxp.pro: sharedmidistate.h is a header
MRI-Binding: Add crude 'rgss_main' implementation (RGSS3)

No F12 reset yet.
MRI-Binding: Bitmap: 'draw_text' and 'text_size' should call #to_s (RGSS2)
MRI-Binding: Bitmap: Bind missing RGSS2 methods
Etc: Implement missing RGSS3 functionality (and bind in MRI)
Viewport: Add zero arg constructor (RGSS3) and bind in MRI