Polish & upgrade the Android Tools demo app

[zmarkan]

The demo app needs some visual and functional improvements to be more in line with the iOS version.

• Update target Android version
• Fix Crash in demo app when adding disk usage health metric provider #93
• UI improvements

[bplattenburg]

@rajramsaroop do you want to tackle this together with your work in #24 ?

[rajramsaroop]

I think it might be better to keep things separate for now, that way someone could tackle the above issues quicker if I don't get to it sooner. I have a few questions about the above bullet points:

• What does updating the target android version get us?
• What UI improvements need to be made?

[okdistribute]

It sounds nice to have, but I am not sure how many developers actively use this, will this fall into the backlog?