Misc bug fixes

- fixed a bug where the dialogs would disappear in Qt version before you could
    use them
- added a fix for supporting a change to the astropy API for coordinates
    having an attribute name change from 'degrees' to 'degree'
- added a fix for an error message in the Qt version in the Zoom plugin for
    uninitialized window dimensions
Merge remote-tracking branch 'origin/master'