feat: first iteration to implement zoom level persistence in DB

[vladox]

Also implements hide_latlng for streamfields
Fixes #85

[marteinn]

Hi @vladox and thanks for the PR! Sadly I cannot accept it because of:

• The string format SRID=5432;POINT(12.0 13.0) is a string representation of a geo point and is done by Django/Postgres, extending upon it to include additional values would break compability
• The zoom feature only works for non-spatial fields, this is due to the zoom being stored on the geo point string representation. This kind of feature would need to work on both spatial and non-spatial fields.

Widgets in Django/Wagtail are a bit tricky to work with, but I think a better approach would be to use a hidden input field that handles the zoom value (we have a similar approach for the location search field). Another way would be to introduce some sort of meta field (for values not related to location), this field could be of a json type and contain zoom and other arbitrary values.

Apologies for not accepting this PR, it's always a good idea to contact the maintainer if you plan on building a larger feature :)

When it comes to implementing hide_latlng I think it's a good idea! Will look through your PR and see if I can make a commit out of it. Will keep this PR open until I have done this.

/ M

[marteinn]

hide_latlng is now implemented in GeoBlock. 0c0a3c6. Thanks for the help @vladox!

When it comes to the other part of the PR (persisting zoom), I'm closing this with my reasoning on the comment above, but would be open to review a PR with another approach!