Bump version and assembly version numbers from 0.7.5 to 0.7.6

This is mostly Bluewall's work but I am also bumping the general version number
OpenSimulator 0.7.5 remains in the release candidate stage.
I'm doing this because master is significantly adding things that will not be in 0.7.5
This update should not cause issues with existing external binary DLLs because our DLLs do not have strong names
and so the exact version match requirement is not in force.