Replace class based lookups with data-target references

Fix #444.

Not sure if this would be considered a breaking change or not. I suppose Varify might rely on some of these selectors. If we want, we can leave this PR open and it can be merged into the 3.0 branch once that is created/

Signed-off-by: Don Naegely <naegelyd@gmail.com>
Closing bracket is missing. Also, the term `toggleExpanded` is actionable.. which is more appropriate for methods. Elements that invoke those actions should be nouns, such as `expandToggle`.