Enhancement/#2 standalone registration

[claasklar]

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• [x] My commits are in nice logical chunks with good commit messages
• [x] My changes are rebased on the latest development branch
• [x] A yarn ready run passes successfully (more about tests here)
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Description

This PR introduces the possibility to register a Signal-Desktop instance as the primary device. For this the entry for opening the standalone registration view is now added to the menu in the production version as well. The tests for the menu are changed accordingly.

resolves #2