As a user, I want to be able to leave comments about dishes and restaurants.

Description:
Patat does not allow any user feedback regarding the data provided.

Checklist
- [x] database changes
- [x] everybody can view comments
- [ ] order comments by date; most recent comment first
- [x] comments go along with username, date
- [x] comments should be limited to 5000 characters
- [ ] comments can only be written if user is logged in
- [ ] if user is logged in, there is a textbox below existing comments to a restaurant/dish to create a comment
    display comments in restaurant view below restaurand/dish but collapsed by default (just showing the number of comments there are)
- [ ] implement a new control that supports character count and use it for creating comments
- [ ] if a dish is deleted, its comments are deleted as well