Makenemo cleaning

While trying to understand how makenemois working, I found several repeated actions (directories/files creation/edition), useless defined/exported variables and slowing down due tu useless loops. Consequently, I tried to rewrite partially the "configuration phase" of the makenemo script in a more simplified and understandable way (at least to me). If @devs find this version cleaner and faster than the older one, we can merge it into the main branch.

• removed useless variables & export
• removed duplicated files/directories operations
• removed useless loop