Started rigging up the play screen.  Removed the preview button from create screen, in favour of it auto-updating.

TODO fix the display of the properties widget in read only mode so it doesn't look like it's all disabled, and make the comboboxes update their values.
Fixed layout of Read-Only mode of PropertiesWidget.

Fixed populating of combobox elements in PropertiesWidget.
Check solution now appears only when playing, and not on the preview.
Clicking save now makes a call to validate to the puzzle, and if invalid, displays a message.
Added a validation function to Cryptogram that throws an exception when the plaintext is empty or null.
Added testing for the validation function in the appropriate test cases.
Save button now offers some feedback:  If the save is successful, a message is displayed, and the user is returned to the welcome screen.
Removed all author identifiers from presentation layer.
Edited the default constructor for puzzle to have a default name, category, and difficulty.
Added scrolling to the puzzle display.  Known bug:  The cryptogram always wants to attach to the top...
Fixed scrolling issue, added wrapping to plaintext box, added limit to text in plaintext box, made the cryptogram not reset its key all the time.
Changed magic number 10 to MARGIN in the cryptogram layout code.
Refactored the Save button's error handling:  The success case is now inside the try-catch block.
Merge pull request #19 from williamhc/rig-up-play-screen

Rig up play screen