Bug fix and minor usability improvement

	modified:   src/main/java/edu/ucla/sspace/gws/GenericWordSpace.java

Fixed filtering logic where the EMPTY_TOKEN type was still having its semantics computed

	modified:   src/main/java/edu/ucla/sspace/lsa/LatentSemanticAnalysis.java

Added a convenience constructor for when someone just wants to say how many dimensions and which SVD algorithm to use.