jquery.tablesorter: Add ability for cells with colspan in tbody

jquery.tablesorter: Add ability for cells with colspan in tbody

* Add manageColspans() to handle colspaned cells in table body.
  Add config.columns - number of colums with extended colspan, inclusive unsortable columns
  buildParserCache() iterate for all columns (not only the first body row, Bug: T105731)
  buildCache() also (Bug: T74534)
  Rows with not enougth cells get after first click additional empty cells.
* Clear unused header data 'sortDisabled' .
* Add $.tablesorter.getParsers() for better table diagnosis.

fix 3 litle bugs:
* Improve multi column sorting with colspan in header (add columnToHeader[..] to s[0] )
* Unsortable headers get after sorting no title tag. ($headers contain only sortable headers)
* Parser detection in tables with max. 5 rows and empty cells works now.

Bug: T105731
Bug: T74534
Change-Id: I518029616d4c10a48eeaad8e92962f4e580f9413