Controls:
• Select elementary flow - Left mouse click
• Move elementary flow - Left mouse drag
• Add currently-loaded elementary flow - Right mouse click
• Load uniform flow - 'u'
• Load source flow - 's'
• Load vortex flow - 'v'
• Load doublet flow - 'd'
• Switch between flow representations (velocity/stream/potential) - 'space'
• Clear all flows - 'c'