Re-work the communicator timer

[pklampros]

As raised in PR #414, the application hacks time_t, a type that usually stores Unix Epoch time i.e. in seconds to actually store milliseconds. The hack was probably applied to easily provide faster updates of UI elements (progress bars) under one second, but should now be changed to a modern implementation such as std::chrono.

It might be worth completely removing the qtimer function altogether if a better implementation exists for such interval testing, instead of having to keep track of a time_t variable that is completely external to the function and to the communicator that is typically affected by it.