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
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
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
Compatibility: Characters can always walk through each other on < 2.54. This fixes the partner character not walking into the old man's apartment in Pleurghburg.
Merge pull request #57 from s--d/linux-fixes

Switch Allegro driver to GFX_XWINDOWS* family for Linux
Merge pull request #58 from s--d/linux-fixes

Engine: Permit Allegro auto-detect ("magic") driver for Linux at compile...
Linux README: Update version number in commands.
Windows: Added ALLEGRO_NO_ASM compile flag for Debug build
Consistent version in Engine and Editor: 3.30.0.1130
Fixed mistake in version representation.

Final version number: 3.3.0.1130.
Engine: fixed exception message

Exception in exception handler... irony of that.
Updated Copyright.txt

Added few more contributor names, sorted in alphabetic order.
AGS.Native: fixed using uninitialized AssetLibInfo object