UI: Add density view in theia-trace-extension

[ankusht-work]

• Trace server now supports density view data-provider with a "new type".
• This "new type" needs to be added in TSP
• Front-end needs to check this "new type" and instantiate a new view (not under the time-axis)
• Evaluate whether D3 makes more sense instead of chart.js

[hriday-panchasara]

Picked up by Traviz