Matrix nodes, new designs, and new major features

Some major additions and improvements, besides better examples/nodes. In particular:

• new linalg package containing nodes representing most basic matrix operations with nice interface
• two new designs
• heavy improvements in the appearance of source code files, which makes programming nodes much cleaner
• new variable update system: you can now create connections between script variables and methods, so that every time the variable changes, the connected method gets called - which enables much more responsive components that automatically adapt to change of data
• a matplotlib example node
• new internal design management system, it's easier now to create new designs, so there might be a few incoming
• passive mode for set var node
• and a long list of small fixes and improvements