Adds ability to save and load projects

[alexhroom]

Adds the ability to save and load both existing projects and RasCAL-1 projects. Fixes #21, fixes #22, fixes #23

• Refactors the project dialog to a base dialog and subclasses for NewProjectDialog, LoadDialog, and LoadR1Dialog.
  • The load project dialog LoadDialog also provides a list of the three most recently saved projects that still exist.
• A project can now be created in a folder that contains things so long as it doesn't contain project/controls files.
• Adds Load, Load R1, Save, and Save As options to the menus.