Properties dialog: select newly added or edited keys automatically

[akks]

Currently after we add some tag or edit it by Alt-A or Alt-S, new tag is not selected automatically in Properties table (except changing name of existing tag to another existing tag).

I tried to improve this behaviour. Now if user edits or adds some tag, it will be preselected in properties table.

PropertiesDialog seemed far too big for me to edit, so it was split into PropertiesDialog (ToggleDialog GUI and events) and TagEditHelper (add and edit windows, autocompletion, applying changes). Now they can be modified separately (I planned to add multiple recent tags adding).

Please see the changes of the code and behaviour. I hope it is more convenient, but maybe I missed something.

[akks]

In 5633/josm:

see #8293: Auto-select edited or added tag in Properties table, refactoring of PropertiesDialog
(TagEditHelper introduced)

[akks]

Further refactoring was done in r5636 , see #8024. Hope that no bugs will arise.

[akks]

Reopen if needed.