Feature: Add a "default map view" setting

[fpapado]

Is your feature request related to a problem? Please describe.
A core use-case of this application is people moving to different places.
Imagine a case where someone has had a lot of pins in country/city X, and moved to Y.
They might not want all those pins skewing the map!

Describe the solution you'd like
There could be a "default map view" option (two boxes, with validation), that allows the user
to set their map view. There might also be help text as to how to get the location of a city.
Then, we would set two layers of views in leaflet-map:

• defaultLatitude/defaultLongitude, which will be picked if...
• fitToMarkers is set to false or undefined
• If not default or fit is specified, then fitWorld