Remove old groovy stacks & update branch names

- Groovy: remove of 3 old (unmaintained) stacks, and replace with new one.
- Hydro & Indigo: Fix wrong branch name in Indigo; now we'll use the same upstream branch for both releases as long as it's possible. 
tl;dr --> Yes
But after reading many ROS docs, I'm still quite unsure about these points (please, head me to anyone else I might ask): 
- if the pkg (mrpt_navigation) didn't exist in groovy, is it 'correct' to add it now to groovy? (I guess it is)
- Our pkgs build & work (or we're working on that!) in both indigo & hydro so, is it 'good practice' to keep one git branch for both distributions?
- In that case: would be 'master' a better generic branch name instead of 'indigo-devel', as I assumed here?