Squashed commits:
[e05e712] Rename Mentors to Mentorship instead of Mentor
[a694422] Fix PEP
[16ecef4] Add 'mentor achievement' to member profiles
[dd10f23] Fix the string format

Gave an exception when saving the model in the admin
[88717d0] Add admin for the mentor model
[08eb778] Change mentors to mentor (all models are singular)