This PR is aimed to make the method behaviour more predicatable, consistent and to slightly simplify the codebase.

The state before this PR is the following:

• Methods makeHidden and makeVisible are featured on documentation and tested, addHidden and addVisible are not. And each of add* only has a single use in the codebase.
• Method makeHidden may produce surprising results on an edge case:
  • Calling makeHidden['col1'] on a model that has $visible = ['col1'] would clear (and thus disable) the whitelist, making everything visible (except col1).
• Method addVisible may produce unexpected results on two cases
  • If the model's $visible was empty, addVisible('col1') will make everything but col1 invisible;
  • If col1 is hidden, addVisible('col1') would not make it visible.
• Other than the three quirks above, the differences between makeHidden/makeVisible and addHidden/addVisible are just these:
  • make* returns model, add* returns void.
  • add* accepts unwrapped lists of arguments ('col1', 'col2') in addition to single string ('col1') and arrays (['col1', 'col2']) which are accepted by both.

To solve the inconsistencies and surprises, simplify the work with the methods and reduce amount of similar methods, I propose here to:

• Make makeHidden and makeVisible accept unwrapped lists of arguments ('col1', 'col2') in addition to current ('col1') and (['col1', 'col2']). That's for convenience and consistency with methods like with().
• Remove addHidden and addVisible.
• Move previous addVisible logic into makeVisible (it's still one line).
• Simplify makeHidden to only add entries to $hidden, but not remove the from $visible.

Explanation on the final point: adding to blacklist $hidden is enough as the blacklist is applied last. The only case where removing from $visible would affect behaviour is the aforementioned quirk that makes everything else visible and such behaviour just shouldn't be here.