Control export email notifications with a setting

Added a new `send_email` boolean to `settings.yaml` that controls whether or
not journal entries will be added to Redmine tickets after export. The addition
of a journal entry triggers email notification of ticket watchers.

Closes GH-8.
support for mapping Redmine ticket types to JIRA

A `:ticket_map` has has been added to `settings.yaml`. This allows Redmine
tracker names to be mapped to JIRA ticket types.

Closes GH-9.