Introduce FormPlugin

index - grouping of includes; highlighter / editor / demo
LRTEditor.FormPlugin - introduced for submitting highlighted code
LRTEditor.MinimalPlugin - bugfix; shift tab should be preventDefaulted
LRTEditor.UndoPlugin - move initial buffer to constructor
LRTEditor - make line-wrapper configurable, disable spellcheck
*.js - made newlines more consistent
style.css - move demo code to index, remove unneeded border