[1262] basic image upload functionality
[#1262] fix how url field is handled
[1262] use logic instead of requests
[#1262] fix test failures
[#1261] add filesize limit, make storage folder backwards compatable, document a bit more
[#1262] First working version of the JS module for image uploading
[#1262] Adds in doc blocks into the image_upload JS module
[#1262] Adds support for different field names for image upload
[#1262] make tests pass
[#1262] only allow file already exists errors to not raise exception
[#1262] only allow file already exists errors to not raise exception for other case
[#1262] fix pull request issues
[#1262] fix required field in wrong place
Merge branch 'master' into 1262-org-group-image-upload

Conflicts:
	ckan/lib/helpers.py
	ckan/logic/action/create.py
	ckan/public/base/css/main.css
	ckan/public/base/less/forms.less
	ckan/templates/group/snippets/group_item.html
	ckan/templates/organization/snippets/organization_item.html
Merge pull request #1262 from okfn/1262-org-group-image-upload

Upload for group and organization images.