MiscUtil: Optional support for Sentry logging

	* Capture exceptions in register_exception
	* add raven to requirements-extra
	* add CFG_ERRORLIB_SENTRY_URI to config, used to set sentry uri and enable/disable sentry feature.

Signed-off-by: Fredrik Nygård Carlsen <me@frecar.no>
Merge pull request #1 from tind/sentry

MiscUtil: Optional support for Sentry logging