[provisional] Add form for contact information

[MizukiTemma]

Short description

This PR implements a new form for contact objects.

This PR is not yet finalized. Changes from #3007 have been taken over but are not actual in this branch. Once it is merged, this PR will be updated too.

To Do after #3007 is merged

• [ ] Add the real URL to contacts listed in poi_form_sidebar/action_box.html

Proposed changes

• Add three new boolean fields to the model contact to store whether E-mail, phone number and website must be imported from the related POI.
• Create a new form ContactForm with check whether those three fields match with those of the selected POI if checked for import from the POI
• Create a new template for the form, reusing poibox.html and _related_contents_table.html

Side effects

• Change the field name "poi" to "location" in the contact model to be compatible with poi_box.html

Memo

• The is not yet any implementation to find contents in which the contact is used. Third box "Contact information" is currently only a place hlder. This will be implemented during #2959

Resolved issues

Fixes: #2953

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