Add a bottom margin to ControlLabel

[huyenltnguyen]

Description

I found that ControlLabel (renders a label) doesn't have a bottom margin, and it sits right above the input when combined with FormControl:

<FormGroup>
  <ControlLabel>Name</ControlLabel>
  <FormControl type="text" />
</FormGroup>

We are currently getting a bottom margin in /learn thanks to Bootstrap: https://github.com/twbs/bootstrap/blob/f17f882df292b29323f1e1da515bd16f326cee4a/dist/css/bootstrap.css#L2609.

I think either ControlLabel should have a bottom margin of 5px, or the FormGroup component should add a space of 5px between its children.

[huyenltnguyen]

Closing as this issue will be addressed via https://github.com/freeCodeCamp/ui/pull/466/files#diff-5e64d0cc9c46937489d71595a4efb9d03f22574a0e83ca8b132a8833e03e6c60R55.