Consolidate messages about unsaved changes

We currently have various ways in which we describe to the user to press the "Save" button. I have always found this messaging rather unfriendly, although the reminder has proven to be effective. Its often incredibly wordy, and gives the impression that it thinks I am stupid in the fact that it is saying to press the Save button.

Before

We could easily make this a lot shorter and more consistenct across core. I don't think we really need to hint at the actual submit button. All we have to remind people of, is the fact that they have unsaved changes. So I propose to change it to:

You have unsaved changes.

This would result in a relatively simple message:

After