XD-546 Add fieldvaluecounter display command

  - Added display command with name, pattern and size as options
  - Fixed FieldValueCounterResource to include getFieldValueCounts method.
  - Added display fieldvaluecounter display method that lists the fieldvaluecounters ordered by values
  - Added fieldvaluecounter tests

 - Changed fieldvaluecounter delete command result text to read 'field-value-counter' for better readability
  - Fixed the corresponding test
 - Fixed field value comparator's compare method
 - Used Tail source instead of File source
  - Appending the tweets to a temp file to check for fieldvaluecounter values

XD-546 Fix tests for fieldvaluecounters
 - Enabled "end" attribute at tail.xml source module configurable
  - This allows us to configure the tail source to tail from the beginning of the file
 - Fixed the fieldvaluecounter tests to make use the above configuration