File Tree, resizable panels and more

-added syntax highlighting for
javascript/css/xml/html/markdown/shell/ocaml(using CodeMirror modes)
-added output panel
-added resizable panels for File Tree, Source code editor, Output panel
-switched function for disabling menu items, now it searches menu item
by name(in prev version it searched menu items by index)
-switched to async functions for filesystem io.
-moved Haxe compiler start process part to
CompletionClient/CompletionServer classes.
-moved file tree functions to FileTree class