add log parsing status handling

I added a new endpoint for to list, detail and update the content of job_log_url.
This is mainly used by the parse-log task to update the status of a log parsing process.
In order to do that, I had to refactor a little bit the thclient to let it send arbitrary data instead of s TreeherderCollection.
I changed the parse-log task parameters, so we need to be careful when we  land this on production. We will likely see all the parse-log tasks already in the task queue fail because of the different task definition
Do we need this permission?  Some of the contributors may want to do this, too.  I just want to make sure it's the right policy.