Improve usability and file management of GUI of WPF tracking application

[raedle]

There are a lot of annoying little things wrong with the GUI:

• zooming & panning does only work on the canvas, not when the pointer is above a node
• the canvas provides no orientation when zoomed in (desert fog)
• there is no permanent overview+detail navigation which could help to solve problems of desert fog
• arrows between nodes begin and start in top-left corner of node, so that input and output arrow are hard to distinguish
• the angle of an arrow tip is too big (90°) and therefore they are harder to read. Maybe making the arrows more pointy and filling the tip would improve readability?
• cutting arrows and moving objects around sometimes feels a bit clunky
• it is confusing that opening a node also enlarges the size of the node, so that it occludes other nodes
• handling of z-index of objects is strange. often less interesting nodes are in front and occlude the actual node of interest

File management functionality and icons are confusing:

• it is good, that the last pipleline is opened on startup as default pipleline, but it is unusual that all changes are automatically saved when closing, so that you often unintentionally mess up pipelines
• a standard FILE pulldown menu with open/save/save as... functions like in a typical Windows application would be desirable
• save function should handle file extensions for pipelines property (not just concatenating them to existing file names ".pipeline.huddle.pipeline.huddle")
• the icons are confusing ... maybe just use a standard pull down menu?