Fixed issue with folder names that contain quotes and are being used in a directory table/list popup

If a folder contains a single quote and is being used in a folder directory/list popup
the generated onclick attribute for the insert link contains broken javascript:
onclick="opener.dismissRelatedFolderLookupPopup(window, 3, '/Foo's Bar/whatever'); return false;"

Added a new method that returnes a url quoted pretty logical path. This can be used for the onclick attributes.
Added missing import and a unit test for covering the quoting property
Use django.utils.http.urlquote as it also handles unicode characters
Remove the urlencode filter
Replaced django.template.defaultfilters.urlencode with django.utils.http.urlquote and removed unused import.
Merge pull request #319 from kux/folder_quoting

Fixed issue with folder names that contain quotes and are being used in a directory table/list popup