Remove empty lines from PHP and JavaScript comment blocks

Remove empty lines from PHP and JavaScript comment blocks

This is a pure documentation change. It mostly removes empty lines from
comments (and entirely empty comments), as well as adds a few missing
documentation blocks and fixes a minor mistake. I hope it's ok to have
this in one patch. I can split it, please tell me.

Change-Id: I9668338602ac77b903ab6b02ff56bd52743c37c4