Add go-jira based config loading
Add go-jira based config loading

This commit does two things:

* enables config being read from .jira.d/jira-ui-config.yml files in
  parent paths. Also reads .jira.d/config.yml files as per go-jira, so
  we pick up endpoint et al.
* sets a default 'jira_ui_list' template, and allows override of this. It's too
  easy for go-jira 'list' templates to break this UI (particularly, location of {{key}}
  and eventually the 'labels()'

mikepea/go-jira-ui,mikepea/tessen