Blackberry platform plugin: Implement support for more buttons on HID "mouse" devices (8 buttons)

A short inspection of relevant header files (in qnx 6.5.0) find definitions for 8 mouse buttons. Preceding this update, we support only 3 of the 8 possible buttons. A user with an advanced USB mouse, plugged into a Blackberry tablet, might find good uses for more buttons. One example is Qt::BackButton and Qt::ForwardButton within Webkit.

Software is written, I am depending on the build system to compile and verify.