widget structure revised

widget structure revised (now you can use an object "events" to define
your handler [handleEvents -> events]; this object is available for both
the backend and the frontend)
+ ui.events.fire accepts a new param (forceSend) to force sending of an
event also if this is not active (for example the checkbox always send
to the backend the click event)
+ initial support for mirrorjs mixins (mirrorjs 0.1.0)
+ removed unused var "that"
+ mirrorjs now calls events and props handler with the widget's instance
context
Application designer updated

+ new widget: datagrid
+ removed positioning (relative/absolute)
+ support for arrow keys to resize and move widgets (SHIFT+arrow to
resize; arrow to move)
+ sample application (index.html) is now standalone ( all needed JS are
downloaded from cdn.mirrorjs.com )
+ support for mirrorjs 0.1.0