Create basic plugin and override the license link in the dataset form

Basic plugin that follows the theming tutorial in the ckan
documentation. The plugin adds an additional directory 'templates' where
ckan will look for jinja2 templates.

There is one file in this directory which overrides the ckan template of
the same name/directory structure that contains a block override to
replace the open definition link with a creative commons nz link.
Add a 'Terms of Use' link to the front page.

Since we are adding an additional page instead of overriding what is
already there we have to add a controller which just renders our
terms_of_use.html.

The controller has to be mapped to ckan's routing so we update our
plugin so we add an additional route '/terms_of_use' that maps to our
custom controller TermsController. We've named the route so we can refer
to it later when we override the header link.

The terms_of_use.html has the text copied from the original, but we've
extended ckan's default page.html that way the page will fit in with the
rest of ckan and have links back to the dataset page etc.

We've overriden a ckan template 'header.html' and overriden the block
that controls the links at the top and removed the 'About' link and
changed the link to our 'Terms of Use' link by using the name of the
route we defined earlier
Override user registration template

We add a link to the terms of use and some additional text to the
existing template in the user reg form.
Completely override the search box form

instead of using ckan_extends we have to override the entire form as
there are no blocks to override. This is a copy/paste of the normal ckan
search form with the 'gold price' stuff removed
override dataset form and resource forms

Replace the blocks with the form fields containing the placeholder text
and replace it with our custom place holder text