MDL-40903 cache: converted persistent into persistentdata

At the same time all cache instances were made persistent
MDL-40903 cache: coding style tidyup pre-integration
MDL-40903 cache: Unittests and small fixes for persistent application cache
MDL-40903 cache: fixed up event invalidation
MDL-40903 cache: renamed persistcache to staticacceleration
MDL-40903 cache: renamed loader method to reflect static accelerator