Restructure repo with python template from eScience Center

[CunliangGeng]

Important info

• During restructuring, end users can still use nplinker as before as long as using code from master branch
• master branch will stop at this commit. It'll not change any more.
• Restructuring work will be on a new branch main, and it will replace master as the default branch of this repo when restructuring is done
• After restructuring, nplinker (prototype) will be installable as a python package
• webapp will be moved to a new repo

TODOs

Before restructuring

• check pros, cons and risks Packaging #15 Create independent repo for webapp? #72
• notify all members Important: Stop committing until restructuring is done  #73

Conduct restructuring

• create main branch from master branch, then do restructuring in main branch
• apply Python template from eScience Center
• enable nplinker to be installable python package
  • Remove requirements.txt file #6