FLUID-5457, FLUID-5469: Remove FSS

Removed FSS. The fss directory in the prefs framework is still there and will be addressed by [FLUID-5482](http://issues.fluidproject.org/browse/FLUID-5482)
http://issues.fluidproject.org/browse/FLUID-5469

Also adds a fix for FLUID-5457, which allows for the cross to appear when using a custom default theme.
http://issues.fluidproject.org/browse/FLUID-5457
It's only needed when we make use of an actual jQuery ui widget on the page. On some of the pages we use other jQuery UI dependencies, but do not have any actual widgets on the page. I've actually updated some files to remove jQuery UI css.