Added Marker Clustering support
Merge branch 'master' of https://github.com/wicketstuff/core into wicketstuff-master

Conflicts:
	jdk-1.6-parent/gmap3-parent/gmap3/src/main/java/org/wicketstuff/gmap/GMap.java
Returning this from setter methods.
Corrected whitespacing.
Added null check for setMarkerCluster parameter.
Corrected whitespacing.
Corrected whitespacing.
Added check to avoid adding the JS file multiple times to the header.
Merge pull request #287 from robsonke/master

[gmap3] Added Marker Clustering support