Updated DComboBox

Added
* PANEL:GetOptionData( id ) returns data of id
* PANEL:GetSelectedID() returns id of currently selected
* PANEL:GetSelected() returns text,data of currently selected item
Added DListView_Line SetSortValue

Does what it says, allows you to have a different value for sorting
rather than the text.
Added position parameter to AddColumn

Also removed the unused SetMaterial method for Columns. (what is it even
supposed to do??)
Merge pull request #732 from Donkie/listview

DListView update
Merge pull request #633 from Donkie/comboboxupdate

Updated DComboBox
Update contentsidebartoolbox.lua

Fixes an error when you delete the spawnlists tab ( even to you shouldn't )
DComboBox now sorts dropdown menu alphabetically
Update player.lua

Don't duplicate code, use existing code.
Added waitforenter key for DProperty_Generic

For entity editing
Fixed DComboBox dropdown sorting
Clean up the default SKIN

Initially wanted to edit it, but ended up with cleaning it up.
Update DProperty_Combo to be usable for ent edit
Centered the hide tool menu button
Fixed map being reset on page change in saves