Rename tools/vim/v8.ycm_extra_conf.py to .ycm_extra_conf.py, so every
YCM plugin (no matter if it's VIM or Emacs) should pick it up
automatically.

Also move the common tools/vim/ninja_output.py to tools/ninja/ as it's
also not related to VIM.

Review URL: https://codereview.chromium.org/904143003

Cr-Commit-Position: refs/heads/master@{#26602}