Fixes #6. Tracks will be added after the current track by default
Merge pull request #12 from jaapmengers/feature/#6

Fixes #6. Tracks will be added after the current track by default
Checks for invalid input
Merge pull request #13 from jaapmengers/feature/input-checking

Checks for invalid input
Merge branch 'master' into feature/7-handle-multiple-sonos

Conflicts:
	sonos_additions.js