Use yard-metasploit-erd

MSP-9821
Add inverse options to associations to help with ERDs

MSP-9821

Backport inverse_of changes from GREAT #1 to ensure that the correct
Relationships are shown in the ERDs.
Revert dependent change

MSP-9821
Port more from GREAT #1 to support inverse_of port

MSP-9821

I ended up porting the smarter Mdm::Tag clean up while copying
associations from GREAT #1, but I didn't copy all the supporting
callbacks and methods.
Fix bundler error

MSP-9821

Fix

Bundler could not find compatible versions for gem "activerecord":
  In Gemfile:
    yard-metasploit-erd (~> 0.0.2) java depends on
      activerecord (< 4.0.0, >= 3.2) java

    metasploit_data_models (>= 0) java depends on
      activerecord (4.1.0)

by restricting activerecord's version in the gemspec to '< 4.0.0'.
Land #57, ERDs in YARD docs