Resolve PS1080.ini path based on PS1080.dll's directory

Problem:
- PS1080.ini is read from the current directory, which could be a problem because (1) it would restrict the application to be runnable only in a designated directory and (2) the current directory would be messed up by these driver dependent files. See the OpenNI community at http://community.openni.org/openni/topics/search_path_for_redist_files where I originally pointed out this issue.

Solution:
- Now PS1080.ini is read from the same location as PS1080.dll.

Description of changes:
- XnSensor.cpp:  ResolveGlobalConfigFileName() is modified to resolve the config file's path based on the DLL's directory when the strConfigDir is specified as NULL, and now XnSensor's constructor uses it to initialize m_strGlobalConfigFile.
- XnSensor.h: Comment is added for ResolveGlobalConfigFileName().
- Config/PS1080.ini: Moved to Config/OpenNI2/Drivers/PS1080.ini.

Note:
- Please test the installer (Redist.py) if it deploys PS1080.ini as intended, i.e. along with PS1080.dll.