Real-time tracing built directly into the framework with Perfetto-compatible data format

[shuhaowu]

Things to do before merge:

• Write design documentation
• Write example showing how tracing can be done
• Figure out a better way to specify which trace file to write to. Make it be disabled by default and only enable it on opt in.

Things to do:

• Investigate TraceSpan move operation correctness: Misc fixes for tracing #44
• Make writing to file optional
• Verify protobuf version and shutdown protobuf library at stop: Misc fixes for tracing #44
• Deal with errors when writing to Sink: Refactor TraceAggregator::Run #38
• CPU affinity: Setup CPU affinity for TraceAggregator #37
• Check for dropped packets when flushing to sink indicator system overload: Refactor TraceAggregator::Run #38
• Check for overrun CyclicThread::Loop and emit instant event indicating overrun: Emit instant event when overrun is detected in Loop #45
• Hook up category: Hook up category to track event packets #39
• Rethink and refactor Run method: Refactor TraceAggregator::Run #38
• Make tracing disable via compile options: Compile-disable of tracing #41
• Make tracing be capable of dynamically enabled.
• Merge Thread and BaseThread: Merge Thread and BaseThread #46
• Determine the speed of the tracing in terms of time takes for a single emit (both when empty and when full, when tracing is enabled and when tracing is disabled), and also how much data can be processed by the background thread per second.: Benchmark tracing performance #40
• Investigate if we can use weak_ptr in the App's cache of thread_tracers and deal with cleaning up of thread_tracers when a thread winds down: Tracing should handle cases where threads are stopped #43
• Fix documentations such that images and links show up properly in doxygen: Misc fixes for tracing #44

Closes #17. Fixes #26. Fixes #15.