fixed some warnings issued by JSHint
removed some unnecessary if statements
reordered list of actions in preferences dialog and got rid of eG_PopupImages array
moved responsibility of checking the status of an action to the action itself
simplified the code that updates the status of the reload action
fixed: actions can only be executed if they are not disabled
changed behavior of closeTab action to align it with Firefox's behavior and made that action a DisableableAction
changed condition for closeOtherTabs action to become disabled in order to take into account possible pinned tabs
removed some no longer needed if statements (since actions can only be run if they are not disabled)
turned copyLink action into a DisableableAction
turned copyImageLocation action into a DisableableAction
removed some apparently not needed pieces of code
made actions cut, copy, paste, undo and selectAll disableable
made action pageTop disableable
made action pageBottom disableable
fixed: the list of actions was not showing up in the preferences window (due to a superfluous parameter in a function)
removed a tip do not providing useful information
made small change in the isDisabled function for the undoCloseTab action
rewrote duplicateWindow action and changed its behaviour so that it now duplicates each tab (instead of just opening the currently open URLs)
made copyImage and saveImageAs actions disableable