Add user behaviour monitoring to find out how the app is used

[ironjan]

See https://github.com/piwik/piwik-sdk-android for an open source alternative to Google analytics.

Goals:

• Decide: is Cafete necessary as a restaurant?
• What is more important: switching days or restaurants?
• How often do users look at specific menus/menu types? Does the ordering "default menu > soup > ..." reflect the users' interest?
• [x] Install Piwik
• [x] Create a new website in the Piwik web interface. Copy the Website ID from "Settings > Websites" (id: 1)
• [x] Update AndroidManifest.xml.
• [x] Add jar
• [x] Initialize Tracker.
• [x] Track screen views, exceptions, goals and more.
• [x] Add option to disable user monitoring
• [x] Add "Datenschutzerklärung".

[ironjan]

git submodules can be removed if necessary: http://stackoverflow.com/questions/1260748/how-do-i-remove-a-git-submodule

[ironjan]

gradle does not work with nested subprojects. Therefore -> jar

[ironjan]

Installed a test version (branch 86-user-monitoring-via-piwik).

[ironjan]

Datenschutz: http://ironjan.de/mensaupb-datenschutz/

[ironjan]

Done with release 2.18.0-1