As discussed in https://github.com/status-im/status-desktop/issues/2144#issuecomment-817791172 and https://github.com/status-im/status-desktop/discussions/2145, it's no longer desired
to have different appearance settings across multiple accounts.
Instead, the appearance setting should apply globally to all accounts,
essentially bypassing the individual setting stored in status-go.
This commit introduces a new global setting called `theme` which,
at the time of introducing this commit, can be either:
0 => Light
1 => Dark
2 => System
Because those enum values matches the `AppearanceContainer.Theme` enum,
this commit removes it completely and simply relies on QML's built-in
`Universal.[Light|Dark|System] variants respectively.
Closes#2144
Pascal Precht
Jonathan Rainville