Merge pull request #5 from ingokegel/2.0

Compatibility with Vaadin 7.0.0.rc2
PopupButton is now a SingleComponentContainer
Correct versions for dependencies
Renamed Root -> UI
call setOwner for VOverlay
Cleaned up server-side API
PopupButton 2.2.0
Support for Vaadin 7.1
Version 2.2.1
changed project to use sbt
Adjustments to build
Refactorings, bugfixes
Updated configuration to work with the most recent sbt-vaadin-plugin
Use sbt-vaadin-plugin version 1.0.0
  * Don't add scala jars because this is a java project
  * Don't compile widgetset on resource generation
Add popup to the DOM only when popup is visible
 * Use Java 1.6
 * first attempt to make shortcurts in popup to work (needs testing)
Version 2.3.0
 * Support for defining opening direction for the popup
 * version 2.4-SNAPSHOT
Use spaces for indentation