Adding config validation to fix #834.

Besides that ticket it is clear that many issues opened that stay open for a long time
has as origin this issue. Users misconfiguring things and not being able to easily figure
out which dependency they are missing.
Reraising the exception with the same stack trace as before as per @dcramer suggestion
correct indentation
Improve validate settings and correct tests
Correct system_frames value
Note autocommit for postgres users
Clean up some queueing documentation and deprecate SENTRY_USE_QUEUE
Styles the team dashboard
indent