GSoC ideas wiki page gardening

[Ilmari Lauhakangas]

Our GSoC ideas page needs some work. This year, projects can be medium 
(175 hours) or large (350 hours). I marked all the existing ideas as large.

We need some medium ones as well, so please consider either adding new 
ideas or splitting old ones (can be 175 + 350 split, if you rethink the 
scope).

These ideas are missing mentors:
https://wiki.documentfoundation.org/Development/GSoC/Ideas#Improve_UX_for_deaf_people
https://wiki.documentfoundation.org/Development/GSoC/Ideas#In-app_rating_.2F_un-structured_feedback

Ilmari