Implement UI for a server list in DeltaClientGtk

[ninjadev64]

Description

This PR implements UI for a server list in DeltaClientGtk. It may be followed with another PR that implements actually storing servers, but as of this PR they are not persisted.

Fixes #183

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation comments
• My changes generate no new warnings

[stackotter]

Looking good so far 👌 The UI feels surprisingly smooth given that SwiftCrossUI is still pretty WIP. Apart from the review comments I've left, the only other thing is that it'd be nice to be able remove servers from the list, but it's all good if you don't want to do that in this PR.

[ninjadev64]

All done 👍

[ninjadev64]

I'll add removing servers later today so don't merge yet

[ninjadev64]

Actually nvm, I'll add removing and editing as part of my next PR - feel free to merge.

[stackotter]

Thanks for implementing this! 🎉 It'll be cool to see the Linux UI progressing a bit more. I might start using it as a testing ground for SwiftCrossUI