Feature: Added Execution timeline

[jelen07]

Intentions

It would be nice to have an execution timeline in Tracy that shows the different parts of the application, how long it took, etc.
At the same time, support for Server Timing API could be added, so you could see the times without whole Tracy enabled including communication with external services.

Merits of this feature

1. Tracy has always been a leader in tuning. As time passes, competitors are adding more features that would be useful to have in Tracy to conveniently debug applications under development.
2. Suitable for smaller projects or smaller teams that don't use external debugging tools.
3. A more comprehensive view of what's going on in the application.