Document formatting does not remove double spaces in imports

[MikhailArkhipov]

import  os
import  class1

Format document -> spaces remain. Yapf/AutoPep8 turn them into a single space.

[MikhailArkhipov]

microsoft/python-language-server#10

[MikhailArkhipov]

In favor of #4698

[MikhailArkhipov]

Since 90% of the code is actually managing UI - formatter selection and installation + packaging, there is very little to do in the LS. VS Code extension already implements formatting with formatter selection and we suggest PTVS to do the same something similar. The remaining code is basically save file to temp, call formatter, read the result back.