[Fluxus] more freeframe commits

[gabor papp]

hi all,

i committed some more features and fixes to the freeframe plugin code. 
typing (help "ffgl") in the console should explain the new features.

briefly, activate/deactivate a plugin, mixer plugins are supported (so 
you can mix multiple pixel primitives together), plugin extensions are 
not required to load a plugin anymore (so scripts can be cross platform).

best,
gabor