Change film rating method to ranking

[cknaut]

Following multiple user feedback, the current movie ranking method is not transparent, specifically:

• It it unsure how the 5-star rating is mapped to a vote (does 3/5 mean a neutral answer)
• Most people don't have strong opinions on all n movies, thus it should be possible to leave movies unranked.

One option to implement these changes while also avoiding any obfuscation of the ranking based algorithm is to provide a drag-and-drop solution, where some movies can be ranked. Possible JS library which can be used is:

https://johnny.github.io/jquery-sortable/

[cknaut]

Decided to rather offer some background on how the rating works and to avoid having to rank all movies.