Added a function for (re)running a set of test cases
Added API for adding, removing and updating tests in internal storage
FileWriter now ouputs new or failed tests to .json
FileReader now supports deletion of tests read from JSON but not from .txt
Generated identifiers are now stored in the internal structure

Test case identifier generation now takes parameter values into account.
In order to be able to compare tests using identifiers, they must be
stored internally, as parameter values may change during execution.

Also, added a catch-clause to handle the case when Add/Update/Delete
Tests is called with no internal storage file existing