Introduce sniff to assert whitespace after control structure

The coding conventions for php state:

    Control structures such as if, while, for, foreach, and switch,
    as well as the catch keyword, should be followed by a space:

This patch adds a sniff to assert the space exists.  A recent patch,
I29867ffdffdfb7d2b56997e9393497c7dc12f7d3, fixes occurrences of this
in mediawiki/core and as such is safe to be used by Jenkins within phpcs.

Change-Id: I602cb6cfe910fc0a9bc371c512ddc591a6a13b26