fltk/, Ui/, Ui.BlockC

• fltk exports a (mostly) stateless C api, and sends events back to haskell.
• All GUI operations must happen from the same thread.
• So actions are shipped over as IO ().
• All modules that foreign import and directly call C functions end with C (and usually .hsc), all non-dependent code goes in the non-C version. Ghci has trouble with the foreign imports.