MapView: Use properties directly

We want to use the gjs property directly instead of the get/set
wrappers. This patch makes MapView only use properties.

https://bugzilla.gnome.org/show_bug.cgi?id=734078
MapView: Use kinetic mode

With kinetic mode turned on Maps feels more smooth.

Thanks to Dario who stumbled over this property.

https://bugzilla.gnome.org/show_bug.cgi?id=734078