Fix issue old issue 301 (https://code.google.com/p/gwt-platform/issues/detail?id=301)

Create pull request from https://codereview.appspot.com/5988064/
Fix some checkstyle issues
Remove trailing spaces

to make checkstyle happy
Fix Issue #192

Add new method removeFromPopupSlot to HasPopupSlot interface
Add corresponding implementation to PresenterWidget
Add test verifying the behaviour to PresenterWidgetTest
Merge pull request #192 from bmoritz/HasPopupSlot

Enhancement for HasPopupSlot
Replaced the Bootstrapper annotations with GWT configuration properties

Fixes https://github.com/ArcBees/GWTP/issues/187
Unlock place manager when async calls fail
Merge pull request #190 from bmoritz/issue301

Fix Issue 301 from https://code.google.com/p/gwt-platform/
Merge pull request #193 from jbarop/issue-187-replace-prebootstrap-annotation

Replaced the Bootstrapper annotations with GWT configuration properties
Merge pull request #196 from hpehl/master

Unlock place manager when async calls fail.
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'