[#1314] Single Solr schema file

To make easier to track changes and simplify the deplyment and upgrade,
the Solr schema file included in the CKAN source is now unified under
`schema.xml`.

As part of the release process, the file will be checked for changes,
and if present the version numbers on the schema file and the supported
versions list will be updated.

Release, install and upgrade docs have been updated to reflect this
changes.

Travis now also always points to schema.xml
Upgrade the OKFN Sphinx theme to the version we had before

Somehow it got downgraded
Merge branch 'master' of github.com:okfn/ckan into 1314-solr-schema-single-file
Add user guide and sysadmin guide to docs toc

These seem to have got removed somehow
Fix a Sphinx warning
Merge branch 'master' of github.com:okfn/ckan into 1314-solr-schema-single-file
[#1314] Fix a Sphinx warning
Merge branch '1314-solr-schema-single-file'
Merge branch 'master' of github.com:okfn/ckan into 1349-tests-for-theming-example-plugins
[#1349] Remove an unused import
[#1349] Typo
[#1349] Rename a private test helper function

So that nose doesn't think it's a test function
[#1349] Rename an example plugin class

Using the same name for this empty plugin class as for other plugin
classes was causing a plugin loading problem when running the tests.
[#1349] Clear extra_template_paths on plugin unload
[#1349] Fix a test setup method
[#1349] Reset ckan.legacy_templates after changing it in tests
[#1349] Fix some HTML parsing in tests
[#1349] Tidy up some test code
[#1349] PEP-8