wip: history refactoring

Conflicts:
	engine/src/main/java/org/camunda/bpm/engine/impl/cfg/ProcessEngineConfigurationImpl.java
wip(history): more refactoring

Conflicts:
	engine/src/main/java/org/camunda/bpm/engine/impl/cfg/ProcessEngineConfigurationImpl.java
wip: support for activity instances
wip(history): add event persistence for hpi & hai
wip(history): add aggregate query for HAIs
wip(history): use ACT_INST_ID_ as ID_ for HAI
wip(history): fix HPI query
wip(history): use business key from HPI START evt
refactor(history): merging changes by marcel wieczorek
wip(activity-instance, history)