Flask Backend Dev

[rNLKJA]

Only merge after all required tasks are done:

• [x] Create a base Flask framework
• [x] Connect with CouchDB
• [x] Create data fetch api
• [x] Create data processing api

[rNLKJA]

I think we need a system design plot, this might be useful for future presentation, we could refer to this GitHub: https://github.com/andyzhao1/COMP90024-A2

As a result, we should have something like this:

@woleigequy @EcZww @RunqiuFeiKM