Changes related to Java version (v7 is now assumed)

- Switched Eclipse .classpath to workspace classpath
- Switched target platform to Java 1.7
- Added Suppresswarnings decoration to TextPatternSequence
(Arrays.asList())
Added handler for p tags to FoLiA indexer.
Started work on TokenFrequency and TokenFrequencyList classes.

These will eventually provide an easier and faster way of determining
token frequencies for groups of documents.