Qt frontend

[Angus Leeming]

It now compiles again. (Sorry Edwin, I should have been quicker to spot why 
things were barfing in the Button Controller.)

A quick test shows that the Citation dialog comes up (and is very pretty!) 
but selecting the FIRST key (only the first) from the list of available 
Bibliography keys causes a segmentation fault. Sorry, no backtrace available.

Angus