genGitHtml split open from resolved

[Chris Warburton]

The pages generated by mhonarc should distinguish between issues'
states. The initial message is always updated to reflect the current
state, which is either:

State: new
State: resolved

We could, for example, loop through the threads, and for each one loop
through the messages until we find one with "State: foo". We can then
alter the HTML to indicate the state in some way, for example prefixing
the subject with '[foo]'.