Revert "refs #9194. Remove custom DisjointElement."

This reverts commit 073d3cc41a8fb65c8fe16dea57d9975b8d408265.
Revert "refs #9194. Get working with boost::disjoint_set."

This reverts commit c33f672fd301ebba7dbba81742e4333f1d7bb86f.
Revert "refs #9194. Try replace custom DisjointElement"

This reverts commit 7b2bd126eba59fba68a4d114381c64e5ff8d14de.