Fix for ActionbarPlus-M6:: M6 macro support is broken (drag and drop) (plus others)

[nfet]

Fixes #377: ActionbarPlus-M6:: M6 macro support is broken (drag and drop)

Misc

• added several functions to ActionbarPlusAPI
• improved ActionbarPlus-M6/M6 detection on drag-n-drop in M6Support.lua and MacroDragEventHandler.lua
• Update code base to use th latest API:IsStealthSpell() function
• removed unused ButtonData.lua
• added support for ActionbarPlus-M6 compatibility check with version of ActionbarPlus