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"
Merge branch 'master' into develop
Merge branch 'develop'