Support change theme in preference panel

[wqz-leo]

Added change theme pop up button in preferences panel.
Allows user to select preferred theme at runtime.
Save selected theme to UserDefaults.
Defaults to system preferences.

Screenshots

License

I AGREE TO THE GITUP CONTRIBUTOR LICENSE AGREEMENT

[lucasderraugh]

We shouldn't be defaulting to a theme one way or the other. In general we should be matching what the system is currently defined as. Now the way I would accept and the way I have seen this work that I think is a good idea is to have 3 options.

On a separate note, was there something about dark mode that you didn't enjoy? Or do you like it but wanted it while the rest of the system was light?

[wqz-leo]

Hi @lucasderraugh ,

I enjoyed the dark mode so much! However, I feel that there might be someone who would like to continue with light mode. At least we should provide an option for them to disable dark mode. IMHO theme preference should be personal but currently there's no option to disable dark mode.

I definitely can add a third option to obey system preference, but I think providing Light and Dark should be good for now. On the other hand, users probably won't change system theme nor GitUp theme very often. Please let me know if you want me to add the third option.

[lucasderraugh]

@wqz-leo I like the idea, but I really need the third option to go with system preference (as the default). As it stands in this PR, everyone is going to be defaulted to dark (even if they use light mode), which is not listening to the system at all. There is also the ability coming in Catalina for the mode to dynamically change depending on time of day (and other 3rd party apps do this today).

So, I'd love the changes, but I'm convinced we need to always respect the system by default.

[lucasderraugh]

Changes needed:

• Compare menu items by represented object or tag
• Have 3 options instead of 2 and default to using the system preference by default (System Preference, Dark, Light).

[lucasderraugh]

Fix the baseline alignment and this will be good to go. Thank you so much for doing this!