RouteService: Add GraphHopper support

Add support for routing via GraphHopper HTTP REST interface.
MapView: add support for showing routes

WIP! Add:
  * clearing of routes
Make route searches via location bubbles

Make it possible to make simple route searches via location bubbles like
in the designs. More advanced searches will have to be made via the
sidebar.
ZoomControl: init in mainWindow instead

Move initialization of ZoomControl to mainWindow.js. It gets easier to
work with GActions and signals if the different widgets are all glued
together in mainWindow.
MainWindow: move Overlay to ui-file

Move the GtkOverlay to main-window.ui and remove the unnecessary GtkGrid.
WIP Add sidebar support