Play Store link & analytics events.

This commit adds the Play Store button along with the App Store button to link
to the Android app. It fires Analytics events for clicks on each of the three
buttons.

Closes #29

Signed-off-by: Joshua Appelman <jappelman@xebia.com>
Removes br tag to horizontally align the app store buttons.
Merge pull request #30 from xebia/play-store-link-second-attempt

Adds all functionality of #29 except for the <br>.