Fix for layout handles order - block generation

[s-hoffman]

Similar to #1263 (That PR includes other changes and appears to be dead, this one is a direct fix for the issue). Also included are comments describing the method flow.

The issue is described quite well in the first 3 paragraphs of #1263 so I will only summarize the changes in this PR.

Changes:

• Calling $layout->getUpdate()->addHandle($handles) prior to the _controller_action_layout_loadbefore event.
• Calling $layout->getUpdate()->load() after the _controller_action_layout_loadbefore event.
• This more closely mimics the flow in Action->loadLayout and related methods.
• (Comments added to describe what is mimicking Action->loadLayout and what is custom)

[s-hoffman]

@miguelbalparda, What do I need to do before this can be merged?