Added missing imports to rmgpy.data.kinetics.__init__ module.

These are needed for some functions in this module to work.
Fixes to the new reaction generation from families algorithm.

The previous algorithm for merging duplicates did not actually work when
forward = False in KineticsFamily.__generateReactions(). This commit
provides a working version, which is rather verbose and repetitive, but
is still better than a non-working implementation.