themes/load! path support prototype

This updates `themes/load!` to take arbitrary paths, so  after re-orging the directories we can do `themes/load!./Button/css/Button` and have it load `./Button/css/ios/Button` and `./Button/css/ios/Button_rtl` (if you are on an iphone/iPad).

I wonder though if a more explicit syntax would be better: `themes/load!./Button/css/{theme}/Button`.  Could do the same thing for RTL too:  `themes/load!./Button/css/{theme}/Button{rtl}` or something like that?   In this case {rtl} is not a simple substitution variable, but implies to load both the LTR file (Button) and the RTL file (Button_rtl). 

Opinions?

Refs #14.