[#157] start backend refactoring.

Initial commit web window crate. Remove common window crate.
3 jobs for window-refactoring in 7 minutes and 48 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #11926
build:linux

00:03:57

passed #11927
build:redox

00:04:13

 
  Test
passed #11928
test:linux

00:03:34