Override the default timeout of Ajax requests

The default timeout (which was wrongly set to 12 seconds) will be reset to 0 (which means no timeout) so that the configured timeout will be effective.
We need to update the front end code in 2 plugins:

• confluence-jira-content, which is responsible for creating a JIRA issue from a highlighted text
• jira-integration-plugin, a cross-product plugin which can be used in any Atlassian products for creating a JIRA issue. Currently, it is being used by JIRA Issues Macro (JIM).
  Check if:
• The timeout won't happen in any browsers.
• JIRA projects can't be loaded when JIRA is down.
• JIRA Issue can't be created when JIRA is down