Documentation of technical decisions

[JanCBrammer]

We need to keep an overview of technical decisions (architecture, frameworks, etc.): what changed, when, and why?

• introduction of MobX-State-Tree: Introduce Mobx-State-Tree for Measurement Tab in Sample chemotion_ELN#848
• ExDev3 Migrate ActiveModelSerializers to Grape::Entities chemotion_ELN#767
• Introduce graphql chemotion_ELN#911