implement Tier0 mode for PhEDExInjector

This one deletes blocks from T2_CH_CERN after they have been processed and have
been completely transferred to a custodial location. If a dataset subscription
exists for T2_CH_CERN then all blocks in that dataset are not deleted.

Since the block check can't know which blocks have been already deleted, it
will search for all blocks in the DBSBuffer, this is limited by creation
date of the block which defaults to two-day old blocks. Configurable
through config.PhEDExInjector.blockTimeout

It also autoapproves the deletion request by default, this can be disabled
by setting the autoDelete option to False in the PhEDExInjector configuration.