Pluggable EE features

Goal

As a developer, I need something that allows me to define a feature as an EE feature. It should be easy to re-define the feature and move it to/from CE.

TODO / How to implement

Some mechanism needs to be present that is used in a feature definition, so:

• in CE version, the feature is "empty" ("locked")
• if possible, there are notes that this feature requires upgrading (like This feature is locked. Upgrade plan + link) -- when an attempt to use the feature happens
• help has to know if it's CE or EE
• build tags to enable/disable EE features
• (optional!) reconsider the implementation of the existing commands

Open questions:

• how to deal with a feature that is available in CE but only partially.
• do we need any changes in configs?

Acceptance criteria

When as a developer, when I develop a new feature, I wrap it so it is easy to define if the feature is EE or CE.