Adding new AGAS cache performance counters

This pull request adds new AGAS cache performance counters for counting the number of invocations and getting the overall time executing various AGAS cache functions. Use them by specifying:

    --hpx:print-counter=/agas/count/cache_*
    --hpx:print-counter=/agas/time/cache_*


Why do we use V1 and not V2 here?