The Github bridge itself should not write anything. This commit removes
code writing to stdout and itroduces an event `ImportEventRateLimiting`
to `core.ImportResult` in order to inform about a rate limiting situation
of the Github GraphQL API. Now the communication with the user is
delegated to the various user interfaces.
* Add NewImportWarning for things that aren't exactly errors.
Use this for unhandled changelog events.
* Add NewExportWarning for things that aren't exactly errors.
Use this for un-exportable status changes.
* Fix git config reader can't read values with spaces
* Add bug-id-revmap config option for the reverse map, and use this
in the importer
* Add NewImportWarning for things that aren't exactly errors.
Use this for unhandled changelog events.
* Add NewExportWarning for things that aren't exactly errors.
Use this for un-exportable status changes.
* Strip newlines from titles on import