[LINTER] Enforce custom coding standard for PHP files

Summary:
These rules are close to Pḧabricator standard.
Requires the installation of phpcs on the local machine.

Depends on D2760

Test Plan:
Should return no error:

arc lint -- arcanist/linter*

Add a tab at the beginning of a line in any of the
arcanist/linter/*.php file, then:

arc lint -- arcanist/linter*

The error should be reported.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: schancel

Differential Revision: https://reviews.bitcoinabc.org/D2764