Generate workbench and editor CSS preferences

Hi Jeeeyul.

I've added some functionality to generate the new CSS from 4.4 for setting workbench and editor colour preferences.

I’ve also made some other commits.  One makes some slight tweaks to the english.  Another commits the generate CoreImage file so as to reduce the number of build dependencies required (I had encountered some problems with your PDE Tools previously). 

The last commit is to restrict the exposed xtext/xtend and guava dependencies from net.jeeeyul.eclipse.themes to only .ui — exporting the packages with no version information is not good practice.  But the better solution would be to consume the bundles directly from Eclipse with version ranges.

This work was sponsored by Takari Inc.