Added 'visible' field functionality for groups

[devalexx]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Feature: adding 'visible' field functionality for groups

• What is the current behavior? (You can also link to an open issue here)
  Currently visible field isn't processed

• What is the new behavior (if this is a feature change)?
  User can hide groups using groups[*].visible

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No, small change

• Other information:
  Should be docs added to the separate repo?

[coveralls]

Coverage remained the same at 89.979% when pulling a144c2a on devalexx:visible-field-for-groups into 721a4ee on vue-generators:master.

[muschottkey]

This seems to be a duplicate of #606.

[zoul0813]

Duplicate of #606

[devalexx]

@zoul0813 @muschottkey
I know that there is a similar pull request. But this one has tests and doesn't duplicate existing function.
But of course it's up to you.