`bp_docs_toggleable_open_or_closed_class()` should be filterable

[boonebgorges]

The default logic is to open on doc create, close on doc edit. But not everyone wants that.

[dcavins]

Fixed via https://github.com/boonebgorges/buddypress-docs/commit/d977b2cedd93826ccb3de001f969bcf6b42ce793.