Add "target" option to menu dialog

Per client request, when creating links, especially external links, there is a need to target the link to open in a new tab/window.

Expected Result: A user adds a new link in the Menu Editor dialog in channel manager and assigns a target for the link. When saved, a new link appears in the menu with a target of "_blank". When clicked, the target of the link will be opened in a new window/tab.

Actual Result: A user cannot assign a target to a link. When saved, the new link is created without a target. When clicked, the target of the link is opened in the same window.

Steps To Reproduce:
1) open any site in channel manager
2) go into edit mode
3) click on an Edit menu button to launch the menu editor dialog
4) create a new External link with a target of "_blank"
5) realize there is no target option available and shake fist in air