Enhancements to the Cesium draw on map tool

[robyngit]

The MVP DrawTool is currently just about complete in the feature-2180-draw-on-map branch (#2180). Once we start putting this tool to use for the plot viewer and geospatial data download, there are some enhancements we can work on:

• Consider showing the drawing interface separately from the side panel (so that users can, for example, interact with the layer list and draw on the map at the same time).
• Add methods for editing & removing points
• Allow creating multiple polygons and other geometries (e.g. rectangle)
• Display a "floating point" under the mouse pointer, such that it's clearer to the user that when they click, a point will be added to the geometry
• Consider automatically activating "draw mode" when the draw panel is first opened

[robyngit]

Some useful feedback that we should address while working on this issue from @rushirajnenuji :

• It was bit difficult for me to understand that the draw was still in process (After plotting the first point of the polygon), it would be nice to have some sort of UI enhancement to reflect that.
• Upon reactivating the Draw Polygon button, I noticed that the tool adds points to the existing polygon. I expected it to start creating another one. (may be I’m drawing conclusions from another similar project that I did in QGIS for KnowWhereGraph, video here if you’re interested)