Rule Editor: Keyboard navigation

[JulienCochuyt]

In the Rule Editor:

• F6 should move focus between the category tree and the selected pane. In the category tree, focus should land on the selected item. In the selected pane, focus should land on the last focused element as long as the selected pane is not changed. When the selected pane is changed, focus should land on the first element.
• control+(shift+)tab should alternatively select same level items of the category tree and loop. When eg. a level 2 item is selected, it should only loop between the level 2 items belonging to the same level 1 node. Focus should land on the first element of the selected pane.

[JulienCochuyt]

Will be part of PR #21.

After testing, it appears that NVDA's MultiCategorySettingsDialog, when cycling through categories, sets focus on the control that had it last when returning to the same content panel - by simply focusing the panel itself. Thus, adopted the same behavior on the new TreeMultiCategorySettingsDialog.

Also added:

• alt+home / alt+end to focus the first/last control on the content panel.
• F2 to move focus from the Properties Pane list to the editing field, and escape to move back to the list.