Schema v1.4, include find directive.

For #376
ModuleInstallDescriptors now have a `find` type.

- `ModuleInstallDescriptor.DefaultInstallStanza` replaces the old one
  in ModuleInstaller.
- `ModuleInstallDescriptor` serialisation options are much more
  explicit.
- `ConvertFindToFile` allows generation of a `file` stanza from a `find`
  stanza and zipfile. (This is our old DefaultInstallStanza repurposed.)
- Tests updated.
- For #376
ModuleInstallDescriptors are standardised to `file` types before install.

For #376.
Tests to exercise new 'find' directive.

More of these would be better... but hey, tests! :)

For #376.
Merge pull request #681 from pjf/376_folder_install

Allow CKAN to `find` file/folder and install it.