Virtual lines for counting vehicles

[LdDl]

• Add control for adding optional virtual line for certain zone of interest
• Download virtual lines from REST API and apply it to the datastorage and canvas
• Upload virtual lines from datastorage to the REST API
• Add control for changing direction detection for virtual line. Could be two states: Left-Right-Top-Bottom or Right-Left-Bottom-Top. This could be useful for counting vehicles on opposite direction or both directions
• Add control for removing virtual line
• Put info about virtual line into configuration section (bottom left container)
• With virtual line rotation/scaling seems like controls messed up (text skew, controls position). Could be fixed in further: may be other PR
• API switcher repaired

Here is laggy GIF (my Peek software lost frames I suppose):

showcase_1.mp4