Add title to logo and cover setting modals

closes #3009

- Added new cover & logo-specific controllers and templates
- Changed general settings template to refer to new controllers and templates
- New templates contain titles, following convention of other modal templates
If I'm not mistaken, this `<section>` and the one in `upload-logo`, `upload-cover`, and `upload` are all the same. Could you extract that into a partial and DRY up the code?