fix(MdSelect): make options in disabled groups un-selectable and fix checkboxes

[VdustR]

• fix(MdSelect): make options in disabled groups un-selectable
  fix [MdSelect] options in disabled groups are selectable #1286
• fix(MdSelect): make multiple selection checkboxes effective
  before:
  
  after:
  

[marcosmoura]

@VdustR Can you resolve the conflicts?

[mdfcorp]

Is there any chance this could be merged? Or is there a workaround for the checkboxes not "passing" the selection for the meantime?

[VdustR]

Yes, I already resolved the conflict.