Implement managed users feature

A managed user is authenticated externally to Sentry, for example
via basic auth by the web server. Such users should not be allowed
to change their username or password from within Sentry.

A new configuration setting, SENTRY_MANAGED_USER_FIELDS, can be
used to further prevent a managed user from changing their name
or email address.
Implement is_regression plugin check

Add a plugin call, "is_regression", called on new events when
the group's status is STATUS_RESOLVED. The call may return
True if this event is a regression, False if it is not, None
to defer to other plugins.

For example, a plugin may wish to examine a tag's values on a
group and only consider the event a regression if it is
contributing a new tag value.
Merge pull request #1261 from jaysoffian/plugin_regression_check

Implement is_regression plugin check
Merge pull request #1255 from jaysoffian/managed_user

Implement managed users feature
Use compact separators when json encoding
Fix broken json tests
Smarter long line trimming in stack traces
Add docstring for trim_line
Don't raise an AssertionError if the column is out of bounds
Move conditional
Force a data dict to be all utf8 all the time
Lint
Correct Group.is_resolved behavior
Fix inverted logic in 1207582b84455df76af68a536610daf3c0fe30c7
Validate ip address with ipaddr

Also now supports ipv6 addresses
Support for dynamic system options
Correct coverage reporting
Correct index
Improve options docs
Clarify delete logic