Exploration dont work for one

[mavroudo]

Exploration query does not work when only one event type is used.
The reason is that in the execution function it extracts the consecutive event pairs from the given pattern. Therefore, it fails to create the required filter in the IndexTable.

Possible solution, add new function in dbConnector that will allow it to filter on a single event rather than pair

[mavroudo]

Made same small changes that resolved this issue in the cluster branch.