change external name to [pix_openni]
fix library location

in OpenNI2, the use is to put an OpenNI2 folder and some lib aside of the program
and to add this local path to linker search path

so to work, you must copy (or symlink) the OpenNI2 folder and the lib you have download from OpenNI website
fix crash when choosing new device on the fly
add DeviceEvent listener
indentation
add a flag related to device connection

this flag is intended to avoid device access when it is disconnected
fix device opening by URI or id
fix initialisation routine