Added support for absolute paths to templates.

I was pretty sure this was already supported in errai-ui, but when I tried it it didn't work.  I made some changes to the code and now it seems to work the way I expect.  I made the code much simpler, which probably means that I accidentally removed functionality I didn't understand.  :(

The way it should work now is that if your template path starts with a / then it is considered absolute.  If not, then the Class's Package is prepended to the path (replacing .'s with /'s).