Cleanup: wgt2allg unit

Removing obsolete variables and functions, moving some to other code units.
Cleanup: removing wgt2allg.h include where possible
Cleanup: util/file unit
Convert some char** to const** to clean up the build process (courtesy of Scott Baker)
Merge pull request #56 from s--d/master

Applying const modifier to function arguments in alfont.c
Script: RuntimeScriptValue::WriteValue() should not write raw pointers
Increased Version number to 3.30.0000
Editor: updated AGS.Native version and DLL
Common, Engine: reworked Bitmap class

Removed abstract Bitmap interface and renamed AllegroBitmap to Bitmap.
Common, Engine: introducing Graphics struct

Graphics type gathers bitmap pointer and drawing settings, such as drawing and text colors, in one toolset object.
This is a transitional change, before incorporating Graphics class properly.
AGS.Native: using Graphics struct
Update Debian changelog with new version number.
Merge branch 'master' of github.com:adventuregamestudio/ags
AGS.Native: fixed room saving

This supplements commit 158507683a3640b5059ee8d98f240df8b3569ba9
Common, Engine: Graphics class

Graphics class is a step towards being more conformant with new Allegro 5 concept, according to which all the drawing is made to the preset target, as opposed to Allegro 4, where the target is defined as an argument for every drawing operation.
As of this commit, there are many cases of excessive graphics object manipulation, which reveal lack of optimization in original code. Those should be refactored in the following updates.
Graphics class uses preset color for vector drawing
Helper functions for preparing transparent bitmaps
Helper function for making a plain bitmap copy
Common: fixed loading of compressed sprite file by SpriteCache

This bug seem to have existed for quite some time already. The only reason it was not noticed is that when game is compiled, a sprite index is included as well, which provides a table of offsets; therefore the sprite file was never fully read. The problem will arise only if the sprite index table is missing, or ignored for some reason.
Script: temporarily disabled check for globalvar references beyond data buffer

"Metal Dead" game fails to pass this check. The error will be suppressed until root of the problem is found.