Bugfix/issue-1103: always display two months on mobile

[danielappelt]

This PR changes the frontend calendar to always display two months on mobile (cf. resolves #1103 ).

Could someone please create the minified version of the affected JS file and add it to this PR? Unfortunately, I don't know how to do it.

[datengraben]

@danielappelt @hansmorb
I created the minified assets via $ grunt dist after installing ruby and the Compass gem.

~/Code/commonsbooking on bugfix/issue-1103 *10 !3 ?3                                                                                                                                                            took 25s Py base at 10:30:58
❯ grunt dist
(node:9809) [DEP0022] DeprecationWarning: os.tmpDir() is deprecated. Use os.tmpdir() instead.
Running "compass:admin" (compass) task

Running "compass:public" (compass) task

Running "compass:themes" (compass) task

Running "uglify:dist" (uglify) task
>> 3 files created 212 kB → 109 kB

Running "babel:dist" (babel) task

Done.

Also I rebased the branch onto master.

[hansmorb]

Das Problem ist, dass der litepicker source eigentlich aus einer anderen repo kommt: https://github.com/markus-mw/Litepicker

Also eigentlich müsste es auch da geändert werden damit es nicht von zukünftigen Änderungen überschrieben wird

[datengraben]

@hansmorb Ich habe wielebenwir/Litepicker#5 erstellt mit der kleinen Änderung.