Degree proposals

Closes #121 
- The conversion of the credits for orientator and co-orientator were done without first verifying if they were valid numbers. This conversion is now done using NumberUtils that prevents errors on integer conversion.
- Some extra conversions were being performed that were not needed and were removed.

Closes #122
- Corrected a bug on List Proposals that prevents the page from rendering. The error was related with the formatting of dates.