Cache github issues details

[soyacz]

We use user token to retrieve details for GH issues. This causes the need to ask for additional permissions upon logging in to Argus and complicates displaying issues.
E.g. copy issues modal won't show details if issue was not updated by client (which is the case for Summary View Widget and happens in View issues list for some issues sometimes).

Idea is to periodically update basic issue details (like assignee, status, tags, title) by querying GH (e.g. by fetching only latest changes or like we do in SCT/dtest in SkipPerIssue feature). Set up cron that will run ArgusCli command which does that.