Add dependency on redmine_base_rspec plugin
Fix error showing up when project custom fields are not set as visible
Project custom fields don't have to be visible to be used as filters
Do not use visibility of project custom filters
Fix incorrect value
Add dependency on redmine_base_rspec plugin so specs are run outside unit tests
Fix potential error triggered in tests when no OrganizationMembership already exists
Require rspec/core instead of rspec in spec_helper, which seems to be not supported in recent versions of rspec
Don't require redmine_base_rspec plugin unless if in test environment
Remove our specific spec_helper in favor of the standard one in redmine_base_rspec plugin