Marking class properties as static

Hi Jennifer,

Nice work on getting threaded replies working in bbPress!

While working on a plugin for BuddyPress, I wanted to reference your plugin to give users the option to either view discussion threads as linear or threaded.

However, when it came time to hook into your plugin for the threaded option, I couldn't hook into your class methods because of the dual usage of static vs. non-static class properties.

Commit 7dde17b changes the properties in the `UCC_bbPress_Threaded_Replies_Loader` class to static as originally referenced before the class constructor.

This allows me to access your awesome class methods when needed.

As for the other commits:
* Commit 816cb47 basically syncs your v0.4.3 changes from the wp.org repo to Github
* Commit d54b6d7 trims some whitespace in the plugin.

Let me know what you think when you have a moment!