Shared Tabs

It is possible to share a custom ribbom between files.
One file might create a custom tab and add a group of controls.
Another file could then add a second group of controls to the same tab.

xmlns:BSN

Add an additional namespace to the <customui> tag.
This allows us to link each XML namespace between different files and add-ins.
It must be the same in each file that is going to share the custom ribbon tab.

tab idQ

Use the "idQ" instead of the "id".
This refers to our qualified namespace and gives us a way to create a shared tab that can be accessed from other files.