PRESUBMIT: Improve PyLint check and add GN format check.

Add pylintrc file based on
https://code.google.com/p/chromium/codesearch#chromium/src/tools/perf/pylintrc
bit tightened up quite a bit (the one in depot_tools is far
more relaxed).

Remove a few excluded directories from pylint check and fixed/
suppressed all warnings generated.

Add GN format check + formatted all GN files using 'gn format'.
Cleanup redundant rules in tools/PRESUBMIT.py

TESTED=Ran 'git cl presubmit -vv', fixed the PyLint violations.
Ran it again with a modification in webrtc/build/webrtc.gni, formatted
all the GN files and ran it again.

R=henrika@webrtc.org, phoglund@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50069004

Cr-Commit-Position: refs/heads/master@{#9274}

webrtc/tools/compare_videos.py

@@ -55,7 +55,7 @@ def _ParseArgs():
                     help='Width of the YUV file\'s frames. Default: %default')
   parser.add_option('--yuv_frame_height', type='int', default=480,
                     help='Height of the YUV file\'s frames. Default: %default')
-  options, _args = parser.parse_args()
+  options, _ = parser.parse_args()
 
   if not options.ref_video:
     parser.error('You must provide a path to the reference video!')