#152: Ensured at least one ColumnSize must be set, both during Construction and with setters. Had to remove constructor with the Widget varargs constructor as the signature would be identical to the ColumnSize varargs constructor. Widgets can still be added after construction using the add method.
#152: Add back (with adjustment) convenience constructor for adding widgets. Remove unneeded @UiConstructor annotation
#152: Remove incorrect call to setStyleName
Merge pull request #188 from smallporgies/master

#152: Ensure at least one ColumnSize must be set