Replace mimetype with content_type in HttpResponses (bug 1020943)

https://docs.djangoproject.com/en/1.6/ref/request-response/#django.http.HttpResponse.__init__
add sizes to preview serializer
no cache for feed items for feed builder (bug 1038339)
nuke feed search serializers for feed builder previews (bug 1038341)
Merge pull request #2323 from ngokevin/previewsizes

add sizes to preview serializer
handle case where preview size not in index
Add missing classes to wrapper around categories in submit page (bug 1039036)
Merge pull request #2320 from diox/mimetype-keyword-deprecated

Replace mimetype with content_type in HttpResponses (bug 1020943)
Remove obsolete & undocumented darjeeling app (bug 1025307)
Merge pull request #2319 from diox/remove-darjeeling

Remove obsolete & undocumented darjeeling app (bug 1025307)
add .mo files
Extract/compile script.  Today's lucky number is 20484.
fix mistake
Link to account lookup for each app author in app lookup tool (bug 907910)
Merge pull request #2318 from diox/lookup-user-links

Link to account lookup for each app author in app lookup tool (bug 907910)
add feed_item_factory and feed_factory to feed test suite
Commit from Mozilla Verbatim by user michael.koehler1@gmx.de.: 1947 of 1947 strings translated (0 fuzzy).
feed es view serializers (bug 1036216)