Tab details view

[jancborchardt]

There’s more and more meta info we have about tabs and which we should add:

• Change tab name
• Share tab https://github.com/xMartin/grouptabs/issues/91
• Currency setting https://github.com/xMartin/grouptabs/issues/65
• Ability to pick who you are from the participants
• Delete tab (choice: local or from server) https://github.com/xMartin/grouptabs/issues/152

For that we could have a sort of "⚙ Settings" icon next to the tab title. Clicking it (or the tab title) would bring up the screen with those options.