use djangocms-maps (for Mapbox support) instead of djangocms-googlemaps

[macolo]

• we currently use djangocms-googlemaps which only supports google maps
• for google maps a credit card is required always, even though all of our (potential) clients are in the free tier and wont have to pay.
• therefore we prefer mapbox
• I propose to switch the djangocms-template project to use https://github.com/Organice/djangocms-maps

[macolo]

cc @victor-yunenko