Benchmark testing

This merge request depends on the testcafe-testing branch to be merged first.

Look at the comparison to see which changes were actually made (most importantly the __tests__/benchmark.test.js and src/connection/MockConnection.js files).

It currently tests the frontend->network processing time, packet number and size, synchronisation size, network->frontend processing time and event number.

Closes #54 (closed).

Reviews by @im2517, @gc4117, @mnr17, @ztw17 and @alh1717 would be highly appreciated.