Add additional diagnostics to figure out points where boomer doesn't complete

[cmungall]

Follow on from

• Boomer: How to deal with huge cliques? #292

It would be great to have -v -vv etc to see where boomer is at. I have a process that has been running 3 days and I have no idea if it's stuck in a particular clique or is generally slow because of ontology size etc

I could just go in and add some printf statements but maybe there is a better way..

ideally there would also be stats added to the clique report - e.g. this clique took 5mins, this one took 2s, etc.

But primarily we can't want for the report if something is hanging, need a verbosity option

[balhoff]

I think better logging is needed. But in the meantime, you may be hitting the bad default for exhaustive-search-limit, which is too high (20). Try setting to 14.