feature/fix-create-collection

This PR fixes some issues on the *Add Collection* screen. In particular:

- Error messages now highlighted in red.
- Automatically selects and displays the *default* template for collections, since this will be the most common choice.
- Shows a loading indicator when a different template is selected, since it's an AJAX call.
- Replaces the placeholder help text regarding templates.

@jazahn Can you review this?

---
[FLASH-151](https://jira.huit.harvard.edu/browse/FLASH-151)