PHPCS: fix up the code base [1] - various small fixes

[jrfnl]

• Mostly whitespace;
• Use parentheses when instantiating a new object;
• Use elseif, not else if;
• Use single quotes when a text string does not contain interpolated variables;
• Use Yoda conditions;
• One assignment per statement;
• Use docblock format for inline @var comments.

Related to #73

[schlessera]

Test failures are unrelated to this PR and isolated to WP 3.7. Merging anyway.