Release v0.1.3

• Ports can now be locked with (Port.lock(), Port.unlock()) to prevent new pipe connections and current pipes to be disconnected.
• Refactored node auto layout logic into the NodeGraph class.
  • NodeGraph.auto_layout_nodes(nodes=None, down_stream=True, start_nodes=None)
• Added BackdropNode.wrap_nodes(nodes=[]) function to fit backdrop size to nodes.
• Fixed BackdropNode.auto_size() function as it was not written with an undo block.
• Cleaned up drag & drop functions.
  example drag & drop strings :
  • 'ngqt://path/to/node/session.graph'
  • 'ngqt::node:com.nodes.MyNode1;node:com.nodes.MyNode2'
• Removed vendor module.
• closed issue #192
• closed issue #195
• bug fixes.