Do not require iiurlwidth when getting thumbnails.

Do not require iiurlwidth when getting thumbnails.

Some file types might not have a specific width/height. As an
example, TimedMediaHandler can specify thumbnails that are
"mid" sized instead of specific width. The requirement for
iiurlwidth was breaking some edge cases with ForeignAPIRepo
and TimedMediaHandler (Specificly with ?embedplayer=yes).

Do not require a width, but also verify that thumbnail parameters
are ok by running through normaliseParams (Formats that require
a width make this function return false if none is specified).

Change-Id: I8bb4c26db56c814ddfbd3e53ca98d05378c2a0bd