Bootstrap layout introduced.

Conflicts:

	opal-gwt-client/src/main/java/org/obiba/opal/web/gwt/app/client/navigator/event/DatasourceSelectionChangeEvent.java
	opal-gwt-client/src/main/java/org/obiba/opal/web/gwt/app/client/navigator/presenter/NavigatorTreePresenter.java
	opal-gwt-client/src/main/java/org/obiba/opal/web/gwt/app/client/navigator/view/NavigatorView.java
OPAL-1886 Workbench layout first commit.