Table: Add columntoggle style option tests
Table: Simplify the way headers are retrieved

This also speeds things up: http://jsperf.com/table-header-selector
Table: Stop querying the table for "thead tr" in a loop
Table: Stop repeatedly retrieving all rows of the table except the first
Table: Add individual-modules tests for reflow and columntoggle

Re gh-5987
Table: Added comment about rebuild() method deprecation
Table: Simplify reflow refresh
Table: Calculate which cells to unlock inside _unlockCells()
Table: Split locked-column-recording/restoring into a pair of functions
Table: Restore both forced-hidden and forced-shown columns at refresh()
Table: Simplify and speed up tests
Table: Make sure column is hidden for testing .prop( "checked", false )

Sometimes the column starts out as not visible, and sometimes it starts out as
visible. Before making sure that .prop( "checked", false ) has no effect, the
column must be rendered invisible irrespective of its starting state.
Table: Check both forced-hidden and forced-visible columns
Table: Expose unlock()
Table: Add comments about this._instantiating
Table: Remove demo-specific classes from grouped test
Table: Ensure correct reflow cells have class "ui-table-cell-label-top"
Table: Reduced line length in individual module tests
Table: Copy "classes" option value instead of extending one object
Table: Separate popup-related functionality

This introduces the extension and moves only the major portions.