Added abort button to Operations dock widget

Notes:

- Made a bit of a mess of my master branch.  If this pull can't be done, let me know.  I'm prepared to delete my fork and start over if needed.

Visual changes: 

- Abort button added to Operation class, appears to the right of the progress bar for each operation
- "Save" menu item re-enalbed upon completed / aborted operation
- Operations QDockWidget is now fixed height to the size of the Operation widgets.  Note that I doubt that it will behave properly for multiple, concurrent operations - have not tested it yet.

Code changes:

- Connected abort button to abort function in View.cpp.  This manages the actual abort on both the document and view sides.

- Restructured the form a bit.  Added a sub-window which acts as the central widget of the main window.  Subviews live in this window.

- Redefined the Operation class as public QObject rather than QProgressBar.  Opeartion exposes getLayout() / deleteLayout() functions to show / hide it's widgets.