1) Fixes grid search and adds example
2) Automates min/max Cover Freq to simplify input

Create a separate class for pure ComputeFstat wrapper, then gives this
as a parent to the other searches. Ultimately, this will allow the use
of the ComputeFstat class without needing the glitch part, for example
for a transient search.

Removes the fully-coherent search which was just a wrapper to CFS_v2 and
all of the `slow' methods which used command line arguments rather than
the python interface.