refactor FluentPrEnTests so externally started processInstances can be wrapped via fluent api

this was necessary, because the current fluent api only supports startProcessByKey. If a process is started via message, it now can be easily wrapped with a fluentprocessinstance.

On the way, I fixed some bugs in the taskAssert, created a JobAssert and introduced unit testing for the fest-assertions module.
add static helper methods for queries
refactor jbehave tests to use FluentProcessEngineTests, CamundaSupport becoms obsolete