Release v0.12.0

• Remove unused imports (#504)
• More Infrastructure changes for the upcoming session detach feature: run server and client in separate processes (#499)
• Restructuring cargo workspace: Separate client, server and utils into separate crates (#515)
• Terminal compatibility: handle most OSC sequences (#517)
• Split layout flag into layout and layout-path (#514)
• Fix behaviour of the clean flag (#519)
• Make distinction clearer between certain configuration flags (#529)
• Resource usage and performance improvements (#523)
• Feature: Detachable/Persistent sessions (#531)
• Terminal compatibility: Support wide characters (#535)