Add joinPaths utility function
Add a global diamondash config
Add diamondash.url() for constructing diamondash urls
Update widget model urls to use diamondash.url()
Fix test descriptions for utils.joinPaths()
Remove stray 'only()'
Support trimming of multiple slashes in utils.joinPaths()
Merge branch 'feature/issue-88-allow-a-url-prefix-to-be-used-for-api-requests' into develop