Add a warning/error system

[TheAdventurer64]

Although it may be extremely hard to code, a warning system would help let users know when they made a accidental mistake, like this:https://share.icloud.com/photos/00IZnFKDxcB0YT2t_oaITT8Pw As you can see, the user forgot to add any tags to the area, and forgot to add a changeset comment.

[dieterdreist]

Josm has some very useful tests and inspiration. For example this is a hand curated list of likely ok or semi-ok tags:

https://josm.openstreetmap.de/browser/josm/trunk/resources/data/validator/ignoretags.cfg