Enabled setting max/min zoom level in declarative map

Created setters for max & min zoom level qproperty in declarative geo map.
The new max/min values are set in the gesture area so the camera data
values set by the plugin are still intact.

Change-Id: I502159c1842238f41c2d598d2fb82c761af9535b
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>