fixes #1794 Rename of app ensure name is unique

Fixes #1794

STR:
1. create a new app, name it something.
2. create another new app, and name it something else.
3. open project menu, and change the second apps name to the first.

Expected: Should not let you save it.
Actual: It makes a dupe of the project in your user menu both pointing to the same project.

STR:
1. new app
2. save it, name it something.
3. rename it using the title at the top of the phone's UI.

Expected: the original name should no longer be a thing. Should just have one project, saved over the last. I changed the name.
Actual: it did a fork and I now have a project saved at the point of the rename.
Definitely worth going with `"You already have an app with this name. Please pick another name for this app."` instead