Feature addition for Random Indexing to allow deterministic randomization

	modified:   src/main/java/edu/ucla/sspace/index/RandomIndexVectorGenerator.java

- Allows a seed value to be set

	modified:   src/main/java/edu/ucla/sspace/ri/RandomIndexing.java

- Exported all the properties to a constructor which makes sense
- Allowed for the Random seed value to be passed to the RandomIndexVectorGenerator

	modified:   src/main/java/edu/ucla/sspace/util/Properties.java

- Added some static utility methods for convenience