Update javadoc.
Refactor closeness String msgs into local fields.
Refactor ShortestPath function description.
Merge branch 'refactor' into shortestPath

Conflicts:
	src/main/java/org/gdms/gdmstopology/function/ST_ClosenessCentrality.java
	src/main/java/org/gdms/gdmstopology/function/ST_ShortestPath.java