Updated fortran + syntastic behaviour

The syntastic checkers (gfortran, ifort) were outdated, and didn't work.

- Removed local gfortran checker, so that the one that comes with
  syntastic is used.
- Updated the ifort checker.
- Set gfortran checker as default.
- Compiler options can be written to a '.syntasticrc' file in the source
  directory of a project.