Added OC.buidQueryString() utility function

Makes it possible to create query strings by passing a JavaScript hash
map and automatically encodes the keys and values.
Fixed filelist unit tests hidden params

Also added dummy table
Fixed download URL in public page

- Refactored download URL building to make it overridable
- Added download URL override in public page
- Added JS unit tests for download URL
- Added OC.redirect() method to facilitate unit testing
Merge pull request #6929 from owncloud/sharing-fixfiledownloadlink

Sharing fixfiledownloadlink