Move gettext mo file generation out of source/generate.py and in to scons:
*Added a gettext scons tool to site_scons/site_tools. This tool provides a gettextMoFile builder, which takes a gettext template file (.po) and compiles it using msgfmt to a .mo.
*NVDA root sconstruct: cause all of NVDA's po files to be compiled to mo files if source is being built.
*Removed locale compilation code from source/generate.py as its now redundant.