Import buildifier

This patch sets up buildifier to run as part of CI. It can also be run
manually via `//tools/lint:buildifier`.

As a consequence, I needed to make the whole repo conform.

Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
Change-Id: Ic41c97b17255813b6c21aef40ab2f8a216683a2c
diff --git a/y2019/control_loops/drivetrain/BUILD b/y2019/control_loops/drivetrain/BUILD
index 2da69ce..a78eab9 100644
--- a/y2019/control_loops/drivetrain/BUILD
+++ b/y2019/control_loops/drivetrain/BUILD
@@ -1,6 +1,6 @@
 load("@com_github_google_flatbuffers//:build_defs.bzl", "flatbuffer_cc_library")
 load("//aos:config.bzl", "aos_config")
-load("//tools/build_rules:select.bzl", "compiler_select", "cpu_select")
+load("//tools/build_rules:select.bzl", "cpu_select")
 
 genrule(
     name = "genrule_drivetrain",