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_*


We have only V1, currently. This version stands for the used API of the counters. What is your rationale to use V2 instead?