JILS-28: Enable Per-Domain Javascript Functionality

The actual implementation probably won't make it into the core codebase (as a system specific repo seems like a better plan) but it seems worth documenting within the core project for the following reasons

- Some minor changes may be made in the core-codebase to support the functionality
- Documentation will probably be created in case others want to do something similar

Essentially, the FR boils down to this;

Output from the script is used on a variety of subdomains, with different filters enabled for each (enforced server side). Where output is being used to provide a customer with an overview of their project(s) it'd be useful to be able to provide a basic form enabling them to add a comment (or raise an issue, etc).

One way to achieve this would be to have multiple versions of the codebase on the JIRA server, but that's a maintainability nightmare, so instead, this FR proposes the following

- Add some hidden elements to the core codebase (commentDiv, possibly searchDiv etc)
- Develop some Javascript which fetches a specific JS file based on the domain name (which will probably be hashed to help prevent scripted discovery of the DS scripts)

Where needed, each script can then enable the hidden elements and populate them with the relevant elements.

Doing it this way does mean that JS would need to be enabled for anyone wishing to use the existing functionality, but also helps ensure that we're not sending a plethora of hidden elements to users who have no need for it (for example, this functionality is unlikely to ever be needed on projects.bentasker.co.uk).

The main functionality I'm interested in, at the moment, is a means to add comments and a means to raise an issue (though the former is more important). How the actual submission works isn't (or shouldn't be) relevant to this FR.