Combine non-empty-if-present and non-empty-value checks

[straker]

These two checks both check the contents of the value attribute (the former only for submit and reset inputs). When it fails it produces a double message about the attribute. We should combine the checks into a single check to get a single remediation message (this means we deprecate the non-empty-if-present check and change the non-empty-value check to use a new evaluate function that does all the checking).

<input type="submit" value="" />

"Fix any of the following:
  Element has a value attribute and the value attribute is empty
  Element has an empty value attribute
  ..."

[marktnoonan]

Just noticed this looking at a report and was about to open an issue, I would love to pick this up and combine the checks if you don't mind @straker

[straker]

@marktnoonan That would be fantastic, thanks!