Split Yi.Dynamic into dynamic-state

YiVariable and YiConfigVariable are now in Yi.Types

getDynamic and setDynamic are now getEditorDyn and putEditorDyn to
reflect that they are for the Editor's dynamic state

bufferDynamicValueA is now getBufferDyn and putBufferDyn, because
dynamic-state uses a State-like monad instead of unsafePerformIO