Changing trigger or action should not reset frame (page) dropdown

[deyan]

• When you change the trigger of a link, the content of the 3rd dropdown (Frame, Page or Script) should not be reset (it is now)
• When you change the action of a link, the content of the 3rd dropdown should be reset only if the new action is of different type (for example, changing an action from "toggle frame" to "show frame" should not reset the "Frame" dropdown, but changing from toggle frame to "Go to page" should reset it.)

[kyli]

• The content of the 3rd dropdown is actually not taken in consideration from the hud, because of bugous equals() method for the LinkAction. The solution is to override it in the actions which have fields in them, so the fields will be looked at.
• The other requirement is currently not easy achievable, since every configuration panel has different instance of the drop down menu.

[kyli]

Implementation done in [6980].