BOOK-453 Notification when project/organisation save was successful

A lot of the changes are just refactoring a little to create some mixins for the basic functionality. This PR:
- adds a class based on model state to the save button - possible values ready, dirty and busy. Someone can add some styling for these states on the save button, or we can use the property for some other UI.
- added a flash message which gets set when the project or org is saved successfully. There is basic styling in the sass for the .flash.success class but it isn't pretty.