[Fix Issue #15683] `readonly` input should not have a `not-allowed` cursor. Instead, this pull request displays a standard cursor and only displays the not-allowed cursor on disabled items.

Revise docs wording to clarify cursor display

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Refs #15410
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Fixes #15555
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to clarify/hint that a ``<label class="sr-only">`` is not the only way
to do it

Refs #11410

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Make sample code match live example
Move <label> out of .input-group into .form-group instead
Change field from Email to Username to make it less redundant, slightly more realistic
Add <label> for Username field for consistency
Fixes #15118

...to actually make it consistent with what I said in the glyphicon docs
section...

Closes #14951 by merging it.

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Closes #14202.

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References #14010

fixing duped IDs

fix ALL the duped IDs.

make example id match actual id

Good catch @juthilo
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