Use actual web layout resource id for "View in browser" function

[jng]

Quoting Zac Spitzer:

the session urls for layouts previews IMHO whilst useful, really needs to be
with studio with a generic url as the session id does expire

This enhancement will use the actual web layout resource id instead of the working (session) copy. This makes the editor functionally line up with MapGuide Studio.

Because there may be a disconnect between the library and session copies of the web layout (eg. The user hasn't saved the changes), a prompt will be displayed to save the current resource if the session copy has unsaved changes, before invoking the "view in browser" function

Note that this only affects the "View in browser" function. The regular preview (from the toolbar button) will still display using the session copy, which reflects the current state of the resource (saved or unsaved).