Extend Http Logs Client functionality.

Add methods for retrieving CT logs STH and accepted root certificates.
Java cleanups.

Remove fulfilled TODO.
Python scanner: Parallelize entries fetching

When enough cores are available, the cpu-bound ASN.1 parsing processes
start idling. Fetch the log entries in parallel.
Merge pull request #49 from eranmes/small-java-cleanup

Some small Java cleanups, no functional changes