Merge pull request #24 from alendit/master

Refactored random string generation (again).
Fixed transaction number counting
Moved rate limiting to workload config
Fixed issue where starting with second phase the duration would multiply with the number of configured workloads
Fixed issue #22
Setting rate limiting for benchmarks separately added
Workload state refactored to a separate class
Merge pull request #25 from alendit/per-workload-queue

Moving rate limiting to WorkloadConfiguration and various bug fixes
Add a possibility to specify a poisson arrival process
<work arrival="poisson">
The default being the regular time interval
- Note: not to be used with high rate phases.