Bug 35070: Add plugin hook template_include_paths

Bug 35070: Add plugin hook template_include_paths

It allows to add paths to Template::Toolkit's INCLUDE_PATH option

http://template-toolkit.org/docs/manual/Config.html#section_INCLUDE_PATH

Test plan:
1. Install the modified kitchen sink plugin:

    git clone --branch template-include-paths \
    https://github.com/jajm/dev-koha-plugin-kitchen-sink.git

2. Run misc/devel/install_plugins.pl
3. Restart memcached and koha
4. Go to Administration -> Manage Plugins
5. Run the KitchenSink plugin's tool
6. Click on "Schedule greeting"
7. Go to Administration -> Manage jobs
8. If you don't see any jobs, uncheck "Current jobs only"
9. You should see a job of type "Unknown job type
   'plugin_kitchensink_greeter". Click on the "View" button
10. Under the Report section you should see "This is the report block"
11. Under the Detailed messages section you should see "This is the
    detail block"
12. Open the browser console, you should see a message "This is the js
    block"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>