Added support for Parastation MPICH toolchains with GCC compilers

`gmpolf`, but `gmpolf.py` already exists today...

In terms of toolchain definition, it seems like there's no difference between `MPICH` and `MPICH2`?

The current `mpich.py` and `mpich2.py` definitions in `easybuild/toolchains/mpi` need to be cleaned up, since they're basically copy-pasted into each other. `Mpich2` should probably derive from `Mpich` to avoid code duplication.

So, then it seems there's no need for `gpsolf` since it's basically equivalent to `gmpolf`? Do correct me if I'm wrong...