SCUMM: Implement original AD AdLib output.

This implements the original AD output and enables it for Indy3 and Loom DOS.
It is not enabled for Monkey Island DOS because it would break multi MIDI
support. However, there are also drawbacks for Indy3. In the catacombs
we were able to play sfx (Indy walking around) and the background music
at once. This was not supported in the original player and thus also does
not work with this reimplementation.

This fixes bug #2027877 "INDY3: Non-Looping Sound Effects".
This fixes bug #1159581 "ADLIB: Adlib Emulation doesn't Respect Volume Settings"
for Indy3 and Loom.
I18N: Move specification of engine specific files to enginedir/POTFILES.

This allows to keep the engines to specfiy the files for translation close to
the engine sources itself.

Thanks to criezy for his suggestion on this approach.
WINTERMUTE: Fix warning
TSAGE: Fixed playing of scanner tones when switching between characters
TSAGE: Corrected usage of quinn and speaker classes across scenes
TSAGE: Clean up of R2R scene 1550 player position tracking
TSAGE: Variable renaming in R2R scene 1550
TSAGE: Further R2R scene 1550 fields renaming
TSAGE: Further R2R scene 1550 renaming, and fixing tracking junk state
TSAGE: Added code to make newly added inventory items immediately visible
TSAGE: Fix cursor when leaving the scanner dialog
TSAGE: Further cleanup for spaceport scene
TSAGE: Fix to the R2R scene 1550 junk display loop
TSAGE: Silence GCC signed/unsigned warning
TSAGE: Silence GCC warning about variable being shadowed
WINTERMUTE: Fix alpha blending with colormod

This fixes numerous transparency effects in J.U.L.I.A.
WINTERMUTE: Fix colormod with alpha blending

Now apply colormod only to the src color instead of to the dst.
The original code did this inconsistently depending on if the
colormod was 0 or not.
SCUMM: Fix COMI regression, after commit 84d1d28373d782464bd46b10abd6b092f7eb6367.
WINTERMUTE: Fix and clean up BaseSurfaceOSystem::finishLoad()

This fixes a couple of cases which fell through the cracks of the
previous chain of conditions, including 16bpp images and 32bpp images
without alpha. The latter partially fixes bug #3600667.
WINTERMUTE: Simplify string matching