[pylint] webapp.py - fix all wrong-import-order messages from pylint

pylint message: wrong-import-order
  Respect PEP8 import order (standard imports first, then third-party libraries,
  then local imports).

pylint message: wrong-import-position
  Do not mix code & imports

BTW:

- only one import per line
- replace licence text by SPDX tag

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>