[Feature] UI customization & onboarding

[wynteryyc]

Is there an existing request for feature?

• [X] I have searched the existing issues

What feature would you like?

• add AMOLED black theme
• add more colours to text bubble setting
• improve onboarding. I sent an invite to a friend and he wasn't sure what to do with it.

Anything else?

• this app is great. keep going please! 🙏