[outdated] Improved access to unitframes.lua

[sirinsidiator]

This file seems to be rather old and a lot of it's content is local and not accessible from the outside.
In order to modify some things like the style of a unit frame, it would be nice if we could access variables and functions that are used to define them.

EDIT: Some examples:

• KEYBOARD_CONSTANTS
• GAMEPAD_CONSTANTS
• groupFrameAnchor
• UNITFRAME_BAR_STYLES
• GetPlatformBarStyle
• IsValidBarStyle
• CreateBarStatusControl
• CreateBarTextControls
• UnitFrameBar
• GetVisibility
• UNITFRAME_LAYOUT_DATA

and many more