Explicitly describe Account inheritance in Plutus models

[ace-subido]

Environment:

• Rails App: 5.1.6
• Rails App Ruby Version: 2.5.1
• Plutus: 0.13

Travis reported an error when running tests for an application we've developed:

$ bundle exec rake db:create db:test:prepare
Created database '<redacted>_test'
rake aborted!
NoMethodError: undefined method `normal_credit_balance=' for #<Class:0x00000000093ada78>
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/activerecord-5.1.6/lib/active_record/dynamic_matchers.rb:22:in `method_missing'
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/attr_encrypted-3.1.0/lib/attr_encrypted.rb:306:in `method_missing'
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/attr_encrypted-3.1.0/lib/attr_encrypted/adapters/active_record.rb:131:in `method_missing_with_attr_encrypted'
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/plutus-0.13/app/models/plutus/expense.rb:12:in `<class:Expense>'
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/plutus-0.13/app/models/plutus/expense.rb:10:in `<module:Plutus>'
/home/travis/build/bloom-solutions/<redacted>/vendor/bundle/ruby/2.5.0/gems/plutus-0.13/app/models/plutus/expense.rb:1:in `<top (required)>'
...

A hypothesis was because the parent app has an unnamespaced Account model. This error seems similar to the one outlined here #94

Since our parent app has an Account model, it's colliding with the usage of Plutus::Account when it's being inherited by Expense, Liability, etc.

After making the change in this commit, the tests have passed for our Rails application

[coveralls]

Coverage remained the same at 94.523% when pulling 26ecb0e on bloom-solutions:avoid_account_name_collision into 00a98af on mbulat:master.