Enable safe marks by default
When uploading safe marks by a manager failed, I revealed that safe marks are disabled by default. There is a special setting ENABLE_SAFE_MARKS set to False within bridge/common.py. Although everybody can easily set this setting to True, I assume that we can just get rid of it completely (i.e. remove this setting and change all places where it is used appropriately). It was introduced a long ago, when associating safe marks was extremely slow, but now this isn't the case anymore.
BTW this rule seems to be violated by preset safe marks that are populated without any restrictions. So, it isn't working well anyway.