Common: update to Stream classes

+ IAGSStream interface for plugins declares helper methods for reading basic types, so that the plugins could benefit from any kind of conversions made during read and write, like endianess conversion and padding control; base Stream inherits IAGSStream.
+ ProxyStream, a base class for stream wrappers with default implementation; AlignedStream inherits ProxyStream.
* Moved few helper methods from DataStream to Stream.
* Reorganized the order of functions in stream classes.
Common: set only stream endianess for DataStream.

Compare stream's endianess against kDefaultSystemEndianess constant instead of object variable.
Engine, AGS.Native: (de)serialization functions use base Stream object pointer instead of DataStream
Common: fixed AlignedStream not working properly in all cases
Common, Engine: use AlignedStream instead of manual padding
Common, Engine: include "stream.h" instead of "datastream.h"
Linux ags+libraries: Enclose everything in quotes in the startscript.
Linux ags+libraries: Describe inclusion of MIDI patches.
Engine: force OPT_NEWGUIALPHA game option for < 3.20 games
Android: Added "Toggle keyboard" menu option.
Engine: reworked script file handles

Script file handles should not be zero-based, because old FileOpen function returned null pointer as an indication of error, and older games could test handle against 0 to know when this function has failed.
Merge branch 'master' into develop
Android: Slightly reworked PreferencesActivity. It now retrieves the game path from the supplied filename instead of the base path + game name.
Android: Prevent activity restart on configuration change for GamesList and Preferences.
Android: Allow starting of PreferencesActivity from outside the app.
Linux: Add options to set rpath to makefile and debian/rules.
Merge branch 'develop'
Windows and Linux: Use StdScale filters per default, depending on the screen resolution. Can be disabled with the option gfxfilter=None.
Enable StdScaleX filters up to X=8.
Autoscaling: Leave at least 100 pixels of height free in windowed mode.