JIRA Issue Macro should support Anonymous JIRA users

Currently, the JIRA Issue Macro seems to contain a limitation - that, unless a user is in the "jira-users" group on JIRA, it is impossible for them to view JIRA issues presented by the JIM plugin, even though the JIRA project in question is open for anonymous browse access.

However, it appears that this is supported in the underlying metadata by adding the "<ac:parameter ac:name="anonymous">true</ac:parameter>" (using the Confluence Metadata Editor).

The only problem with this is that it gets wiped out if you ever perform an Edit/Save on the inserted JIM. Currently, the only solution we've found for this is to reapply the metadata edit.

I believe this could be resolved in a couple of ways

1. the JIM editor sucks in the existing metadata, updates only what's changed and writes it all back out - thus persisting any underlying metadata edits or
2. (my preferred solution) - the JIM plugin is updated to expose the anonymous setting as an "Allow anonymous access" checkbox. The default would be as "unchecked" to replicate current behaviour but ticking the checkbox would cause the insertion of the "anonymous=true" parameter in the underlying metadata. If that setting already exists in the metadata then, when the JIM is edited in the future, it's current value is exposed in the setting of the checkbox.