Allow to configure Jira api URL
Cf. support request 2829
Provide a property api_url
for JiraService
in order to customize the API path. This is necessary if for instance Jira is not installed at the root of the web server. For user convenience, the API URL is automatically built from the Project URL using the same logic as before, so that it shouldn't be necessary for users to actually enter the API URL in most cases.
Remove the api_version
property which seems redundant with the API URL. A DB migration
removes api_version
and initializes the API URL from project_url
and api_version
using the same logic as before for a seamless transition.