Added possibility to create a georectangle from a list of coordinates

It will create the smallest possible rectangle that contains all of the
coordinates. This is accessible from qml using the locationsingleton.
The plan is to include the ability to fit the view-port of the map
to a georectangle.

Change-Id: I616ac8ef169f697e53a3d9ebcf114f4f2cde8298
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>