Add style configuration option to LeadingZero

The `LeadingZero` linter can now be configured to prefer leading zeros
instead of reporting them, which was requested in #92.

Change-Id: I998f32b016b8df8ed87c438424b209da41d2b5f8
Reviewed-on: http://gerrit.causes.com/36426
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>