Updated all files inside lua/vgui/ and also edited lua/includes/vgui_bas...

...e.lua ( make ALL of the filenames lowercase )

Added PANEL:OnToggle( ) Callback for DCollapsibleCategory ( Requested in forums; I supplied an injection for it.. Now it is built in )

All files were checked and had trailing spaces removed,
DERMA header added/updated/corrected( to go with a "standard" so all files looked the same with DERMA and the vgui elements contained within the file listed below, occasionally some notes are either to the right if it pertains to that element, or underneath the elements ),
Function comment block was added/updated to ALL functions ( Many were missing comment blocks, or had improper names attached ),
Maintained single-space between function end and next comment block, two spaces separating two elements within a file,
Corrected many functions spacing ( to coincide with current code-standard "Airy" meaning one space below function/args and one space above function end ),
I wanted to rename dcategorycollapse.lua to dcollapsiblecategory.lua ( the proper name ) but was unable to find the AddCSLuaFile/IncludeCS where it was included,
Removed up to two empty lines at end of file from many of the files.

This is the beginning phase towards getting all vgui files to a code-standard. I ask that other eyes take a look ( I have already tested and no coding errors showed up ) and see what can be changed.
One thing I wanted to look at, was there may be some identical functions called twice in some of the files ( this may be limited to the files that have two or more elements within; or they were already removed ) but didn't notice any.