[#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
Fix documentation for form.select
Update form.html
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.