Bugfixes:
  - unit_store: the "g" case is taken into account
  - units: fill_in_power uses develop_symbol before calculations:
        => no more develop_symbol needed before calling it
  - units: some cleaning: indexUnit no more needed
  - unit_unit: added the test [E] = [m] + [c] + [c] has to be homogeneous to Joules
Merge pull request #67 from SylvainPlessis/unit

Bugfixes

Alright I'm merging this and have a victory coffee for @ddemidov, thanks again