[Code Style] Changes in tag standards: Plugins

This pull should fix the issue detailed here: joomla/coding-standards#80

I have broken in parts this original pull #4590 to make it easy for review. This pull is contains only the plugins.
The rest of the changes are going to be sent in different pulls.

This pull is related to #4603, #4625, #4632, #4636, #4637 and #4617.