Callgraph search and style

[monicawoj]

Resolves #1687 (search functionality for callgraph nodes)

Also:

• applies different color scheme (tested for accessibility using color blindness simulator Chrome plugin "Spectrum")
• provides first letter of function name on nodes
• debounces node search to avoid multiple immediate re-renders of the callgraph/icicle graph

[monicawoj]

To-do: adjust colors to make more sense in dark mode