Removed warnings in docs about MTI Plugins
Create test case for MTI Plugins
Test plugin app for MTI test case
Add test(s) to module
initial migrations for mti_pluginapp
remove dedicated test script
Add tests
Update support files for new test app
fix import typo
Fix makemigrations in develop.py and let it make initial migrations as required

call_command('schemamigration'…) returns a SystemExit when it is complete. Without a try/except block around it, this will cause a loop to prematurely terminate in a seemingly normal way. This is what was happening before this fix, and this effectively caused `develop.py makemigrations` to only ever make migrations for cms, which is the first appliation in the list.

Also, I've added code that will first check to see if an app already has migrations and if not, it will run the equivalent of `manage.py schemamigration [app] --initial` and emit a notice of the same.

Finally, this now detects if an application in the list if not found, and emits a notice of this too.
Fix import issue
Add app to develop
Fix other tests to work with this app active