Add screen on first startup that shows license & instructions to user

[barbeau]

We should show the user a license they need to agree to when starting the app for the first time, as well as a brief tutorial on using the app.

This can be similar to the license and FAQ shown to the user in the MyTracks project.

[vreixo]

I think that would be better than the screenshots some kind of "demo screen": http://stackoverflow.com/questions/12013334/how-do-you-create-a-transparent-demo-screen-for-an-android-app https://github.com/Espiandev/ShowcaseView

[barbeau]

I agree, I'll change the issue name to reflect this.

I'm using ShowcaseView in another app, and its worked well so far.