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 ticket 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).

This way we can have a before/after preview where clicking "View in browser" gives us the last-saved version of the library resource, and previewing via the toolbar button gives us the current version (w/ any unsaved changes).

[jng]

Description changed so that previewing matches how its done in Studio (which the original description was 95% close to)