git-trunk/app: Make the code more idiomatic

Change-Id: 3b0ec23baa
git-trunk/modules/jira: Tweak config

Make config.BaseURL into *url.URL instead of string.

Change-Id: d14d802faa
Story-Id: 78913390
git-trunk/modules/jira: Add some API utils

Implement a few handy functions that build a Jira API client based on
the salsaflow configuration.

Change-Id: e23d902cd1
Story-Id: 78913390