[#790] Tutorial for custom fields in packages
[#790] add custom fields tutorial to extensions index
[#790] clean up formatting
[#790] resource customization tutorial

also added resource example to idataset form example
[#790] add tag-vocabularies to custom-fields tutorial
[#790] fix titles to match docs style guidelines
[#790] custom fields tutorial

move source for tutorial into it's own files
[#790] custom fields tutorial

* Add tests to example_idatasetform plugin.
* Split out source from tutorial into plugins so they can be tested
* Use sphinx referencing
* Add section on validators and conveters
* Minor rewrites, fix titles, etc.
[#790] undo doc subproject commits
[#790] remove unused plugin version
[#790] pep8, fix tests by preventing plugins from loading during import
[#790] IDatasetForm tutorial cleanups
[#790] IDatasetForm tutorial: add dataset search page sorting
[#790] Add IDatasetForm search template
[#790] idatasetform tutorial cleanups
[#790] idatasetform tutorial cleanups
[#790] idatasetform tutorial cleanups
Use the full organization dict to display orgs

The package page uses only the bits of the organization dict that is returned
from package_show, this doesn't have the image_display_url and therefore
organization images are not shown anymore. This uses a new helper to get the
full organization dict.
[#1617] Clean up templates/package/related_list

Stop using the package dict unnecessarily
Fix pep8