few non atomic changes, see description.

Revamped dragging/sizing system to work on all borders and corners
Removed empty function descriptors
Changed a few internal variables(m_ syntax is retarded)
Added SetBorderThreshold(number) to set the size of the sizing area
Added SetMaxWidth/Height(num) which limits the panels size
Minor optimisations
Reverted previously existing accessor func internals to previous name in DFrame.lua