define shared pointer MetaPos::Ptr

MetaPos is derived from QObject, meaning that it is not copyable.
Sometimes, a MetaPos is returned by a function. Without this typedef,
a pointer would have to be returned and the caller would need to take
care of deleting the MetaPos object correctly.

However, to avoid having to take care of deletin, this typedef
delets the MetaPos object automatically if no reference to the object
exists anymore.
refactor: use AnchorManager to show anchors