Make blacklisted_local_types configurable

[coryvirok]

We want to allow the user to configure the blacklisted_local_types object. Currently, this is only done by rollbar.contrib.django when it's imported.

[rokob]

A bigger issue here is that blacklisted_local_types still exists as a list in the code, but it is never used anywhere. It appears that the blacklist idea was converted into the idea of safe_repr which is basically a whitelist. The change that stopped using blacklisted_local_types was #75. So I'm going to close this issue by cleaning up the existence of that list including modifying it in the Django contrib code in favor of the existing whitelist and safe_repr options.