QEMenuButton labelText and font properties

[rfgunion]

At the ALS we use menu buttons in EDM quite a bit, with button labels. This seems a useful and simple addition to QEMenuButton.
Also, the font property was not being mapped to the underlying button in the qegui environment; I added the setFont() and font() methods to do so.
I also found that moc was not honoring preprocessor directives in QEDesignerPluginCommon.h, so I copied the QT_VERSION check into the include files in the qeplugin project (see the comments for a pointer to a possible explanation).

[andrewstarritt]

Hi Bob,
Thanks for the input. I will look at the proposed changes and merge them.
Note: Github is the means by which we make epicsQt public and should be considered a mirror
of the current "master", which is out internal non-git source code repository. So while I will merge
in what I can into out own source code repository and the update Github, I will prob. "ignore" or
"reject" the 'hub pull request itself.

[rfgunion]

Hi Andrew,
Great, thanks! If you'd prefer another way to contribute, let me know!
Best regards,
Bob