Add replay capabilities to the server

[jbarnoud]

Make the server able to serve recordings. Fixes #112.

[jbarnoud]

TODO at this point:

• [x] fix the time management so long delays between frames do not block the simulation thread
• [x] implement step
• [x] handle resets and simulation changes occurring in the recording
• [x] send the state
• [x] adapt GUI
• [ ] Use better UI for the CLI
• [x] cleanup

[jbarnoud]

Things to fix:

• [ ] sometimes, server does not close after ctrl+c
• [x] when resetting, the state should be cleared

[jbarnoud]

I encounter issues replaying a SubtleGame recording:

• the box was not located at the right place, likely Subtle game does not send the right data
• the rendering was not applied, I need to check what is in the recording
• the headset seemed to have soft crashed and lost controller tracking

[jbarnoud]

the rendering was not applied, I need to check what is in the recording

This can be explained by the names of the keys. Rendering keys contain the name of the program, for SubtleGame it is still "narupa".