Add pre-commit config for formatting and linting (#1166)

Adds a pre-commit config for development that runs several fixers, including YAPF with
"google" style and pylint for static analysis.

Use of `requirements-dev.txt` appears to be a common pattern for this
type of work:
https://pypi.org/project/requirements-dev.txt/

src/requirements-dev.txt

@@ -0,0 +1,7 @@
+# This file contains all requirements needed for GAM development work
+
+# Include all build requirements
+-r requirements.txt
+
+# Dev-specific requirements
+pre-commit

src/requirements.txt

@@ -1,10 +1,10 @@
 cryptography
-python-dateutil
 distro; sys_platform == 'linux'
 filelock
 google-api-python-client>=1.7.10
-google-auth>=1.11.2
 google-auth-httplib2
 google-auth-oauthlib>=0.4.1
+google-auth>=1.11.2
 httplib2>=0.17.0
 passlib>=1.7.2; sys_platform == 'win32'
+python-dateutil