Fix race condition when setting currentView

As the front page only serves to work out what to do on load we should
never set the currentView to front-page. However, due to execution order
what actually happens is that the navigation to the front page completes
after the navigation to the actual page displayed. This means that the
incorrect currentView is set and the easiest way to fix is to prevent
the currentView being set to the front page
Correctly handle back button on start screens

On the inital screens the android back button should quit the app, or if
on the map screen and you've started a report it should cancel it. Add
in a default back method to FMSView and an override method for the map,
exising report and offline screens
Fixes #117
remove unwanted debug statements
Make dubug output conditional on a debug flag

Replace console.log call to a wrapper function that only outputs if
we've set a flag in config.