Adding attributes to fieldsets. Legends are optional for fieldsets.

As the comment says: Every collection is wrapped by a fieldset if needed

A legend is not required for a fieldset.
* Now, if a label is specified, a legend will be created.
* Before, a fieldset would not be wrapped around the markup unless a label was set.
* Now, a fieldset will be wrapped around the markup if $this->shouldWrap is true, regardless if a label has been set for the legend.
Adding attributes to fieldsets, this allows for the space.
Merge pull request #5623 from gammamatrix/patch-2

Adding attributes to fieldsets. Legends are optional for fieldsets.
[#5623] More tests

- Added tests covering the various use cases:
  - fieldset without attributes
  - fieldset with attributes
  - fieldset without label
  - fieldset with label renders as legend
- Fixed code submission to only provide attributes in opening fieldset
  tag *IF* present
Merge branch 'hotfix/5623'

Close #5623