Introduce getPermissionKeyDisplayName-Description

Let's add the getPermissionKeyDisplayName and
getPermissionKeyDisplayDescription methods to the PermissionKey class.
They return the localized name/description (so that you don't have to call
tc()) and they optionally escape the name/description in html format,
javascript format (default is to escape in html format).
Remove the json encoding option from getPermissionKeyDisplay...
Merge pull request #1448 from mlocati/add-PermissionKeyDisplayName-Description

Introduce getPermissionKeyDisplayName-Description