Algorithm for deciding which cells handle sorting is exactly
the same as in the real jQuery Tablesorter.
Depends on changes in VE core:
* I50426e173c68af7df49e47fe3bec0465a9a55c26
* Iabb372dfe7bf5feef314315ac74a788c6c58dc20
Bug: T139072
Change-Id: I4446be2ad459b05590754da9bb6c3dd8f796be42