[OPT-1185] Fetching of engine entities is done by timestamp - camunda JIRA

AT:

for fetching the historic process instances|historic activity instances, the request:
- sorts the data by ascending start date
- uses a page size
- fetches all data with a timestamp greater than x, where x is the startTime of the last page entry of the most recent page and 01-01-1970 if it's the first request.
the index handling is done according the previous described procedure
the index storing data structure also has the timestamp mechanism stored
the data fetching is not spread across multiple classes, but has one object responsible for the communication with the engine

AT:

for fetching the historic process instances|historic activity instances, the request:
- sorts the data by ascending start date
- uses a page size
- fetches all data with a timestamp greater than x, where x is the startTime of the last page entry of the most recent page and 01-01-1970 if it's the first request.
the index handling is done according the previous described procedure
the index storing data structure also has the timestamp mechanism stored
the data fetching is not spread across multiple classes, but has one object responsible for the communication with the engine

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