Detect whitespaces issue with Phan

Summary: Phan now provides a plugin to detect \r, trailing spaces and tabs.

Test Plan:

$ echo "  " > src/foo.php
$ phan
src/foo.php:1 PhanPluginWhitespaceTrailing The first occurrence of trailing whitespace was seen here.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2163