bashlib: fill ocrd.process.profile logger

[bertsky]

We are currently blind in our process/profiling logger to any bashlib-based processors (which step ran and how much time was spent).

Implementing this with bash is probably not so easy – you have to keep track of and aggregate CPU-time from all subprocesses forked by the shell through the script.

[bertsky]

IMO this should be done based on the recipe described for the API changes.

So this would require a rewrite of all bashlib processors – but we need to do that anyway. (And the page loop is usually based on our input_files array now, but still clumsy and requires lots of boilerplate.)