GeezerVison

• Add option to cycle column header sorting through ascending, descending and none

• Clicking the header of a sorted column only toggled between ascending and descending order, so removing the sorting required the separate 'Clear sorting' action. A new setting in the Data Browser preferences makes a click on a descending column remove the sorting instead, so repeated clicks cycle through ascending, descending and no sorting. This also works for Ctrl+click, where only the clicked column is removed from the sort columns.

The default behaviour is unchanged.
The decision how a click changes the sort columns moves from TableBrowser::headerClicked into sqlb::updateSortColumns so that it can be covered by a unit test.

• New Record (Ctrl+Shift+N), Delete Record (Ctrl+Shift+D) and Revert Changes (Ctrl+Shift+R) had no keyboard shortcut. The two record actions are limited to the table browser which has the focus, so they do not clash when there are multiple browsers. The shortcuts are also added to the tool tips.
  A test checks that the actions have shortcuts which are unique among the actions and do not shadow standard keys.