Fix EZP-23296: Template Block Cache has cache key collisions

The template cache blocks where using crc32 which has a high probability of collisions.
Feature has been changed to use md5 like viewcache already uses.

Note: To avoid that you have to many cache blocks take advantage of putting identical once in
own template so they will share cache (template and location of block is part of internal unique key).
Merge pull request #1069 from ezsystems/EZP-23296_cache_block_crc_collisions

Fix EZP-23296: Template Block Cache has cache key collisions