Theme preferences not respected

[ChildishGiant]

Expected Behavior

Akira should use the light/dark theme based on the user's choice, although that can be overridden in the settings still.

Current Behavior

The user's preference isn't reflected at all. It appears this functionality has been attempted but it's not working https://github.com/akiraux/Akira/blob/83c7b03b1a29274d46a4811c94ff4a8be4e050dd/src/Window.vala#L93

Possible Solution

https://docs.elementary.io/develop/apis/color-scheme#using-the-users-preference

Screenshots of the Problem

https://user-images.githubusercontent.com/13716824/129961388-3ca39b27-9446-430a-a196-8375498528f8.mp4

Your Environment (for bugs)

Linux elementary-os-desktop-39fa46e2 5.11.0-25-generic #27~20.04.1-Ubuntu SMP Tue Jul 13 17:41:23 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
NAME="elementary OS"
VERSION="6 Odin"
ID=elementary
ID_LIKE=ubuntu
PRETTY_NAME="elementary OS 6 Odin"
LOGO=distributor-logo
VERSION_ID="6"
HOME_URL="https://elementary.io/"
DOCUMENTATION_URL="https://elementary.io/docs/learning-the-basics"
SUPPORT_URL="https://elementary.io/support"
BUG_REPORT_URL="https://github.com/elementary/os/issues/new"
PRIVACY_POLICY_URL="https://elementary.io/privacy-policy"
VERSION_CODENAME=odin
UBUNTU_CODENAME=focal

• Akira Version: v0.0.16 - alpha (appcenter)

[Alecaddd]

Sure, I'll implement this before next release, thanks for the report.

[ghost]

@Alecaddd This should be closed after #657 is merged