ScriptAPI: simplified plugin stubs

Since plugin stubs don't really do anything, and since new script API has uniform function handler type, there's no need to multiply empty functions. It is still important to provide "default" return value, therefore we need only one stub per return value.
Engine: added extra error check to room deserialization

This helps detect memory potential memory corruption early
Engine: safety fix for Interaction destructors
Engine: fixed object's transparency precision loss
Common: safety fix for decrypting asset name

This deals with incorrectly written encrypted asset name that does not include null-terminator.
Also removes the dreaded strlen() call from the loop.
Engine: corrected transparency conversion test
Engine: "upscale" overriding config option

The earlier versions of AGS provided support for "upscaling" low-res games (320x200 and 320x240) to hi-res (640x400 and 640x480 respectively).
The script API has means for detecting if the game is running upscaled, and game developer could use this opportunity to setup game accordingly (e.g. assign hi-res fonts, etc).
This feature is officially deprecated since 3.1.0, however the engine itself still supports it, technically.
This overriding option re-enables "upscaling". It works ONLY for low-res resolutions, such as 320x200 and 320x240.
Fix for moving folders up & down screws up compilation since ids are changed (same problem as in a previous fix for folders dragging).
Merge remote-tracking branch 'origin/release-3.3.0'
Merge pull request #16 from adventuregamestudio/master

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