Show tab ID for sharing also on empty tab screen

[xMartin]

On the main screen that shows the overview and transactions of one tab we display the tab ID for sharing but it is missing in case you have zero transactions, typically when you just created a tab.

Thanks for reporting, @jancborchardt

[jancborchardt]

Yup! Would be ideal to put it as a sticky footer so it doesn’t take too much focus away from the main text and the »Add transaction« button.

[xMartin]

Opened #138 for the sticky footer thing.