There is now only one supported way to debug GWT, so remove the "SDM"
naming, as it's basically an implementation detail. Be consistent
between the launcher and class names,
gerrit_gwt_dbg -> GerritGwtDebugLauncher.
Update the documentation to be consistent as well, and link to the
article about Super Dev Mode.
Change-Id: If541bc48bf828a8af64d631d7acd6f663d5ecea1