Implementing HasWidgets/HasText on any widget that has the setters/getters for Text, so users can use that interface.

Conflicts:
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/Alert.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/Badge.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/Heading.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/Lead.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/LinkedGroupItemText.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/ListItem.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/ListItemPanel.java
	gwtbootstrap3/src/main/java/org/gwtbootstrap3/client/ui/PanelHeader.java