Hogcon

Changes:

1. Removed HogConfig.deadline in app since `HogTrigger` is triggered only during `createSubmission`, and `createSubmission` already checks for hogcon deadline as an assignment.
2. web hogcon page now retrives deadline and year via API request.
3. Add breadcrumb navigation for hogcon page.
4. Local app release places two Ok files, 0.0.0 and OK_COMMIT_HASH. Change the default behavior of MiscController.getOkClientVersion to filter out dummy file 0.0.0.

Now, hogcon no longer needs to be semester-specific, as all of its information is stored and retrieved as an ordinary assignment.