Removed some unused source files

- I don't believe there's a need to keep them if we're not using them.
  If and when we will ever need them again, this commit can be easily
  reverted.

Signed-off-by: Haru <haru@dotalux.com>
Fixed order of includes in all source files

- Changed order according to the (upcoming) code style guidelines.
- Fixes several issues caused by missing headers when their include
  order is changed or in plugins.

Signed-off-by: Haru <haru@dotalux.com>