[WIP][Draw] Remove pause button

[haydar-c]

This PR removes the Pause button from the GUI. The button only had an effect if VPR was already paused (for example, at a breakpoint, at the end of a stage, or due to a previous pause). Since it never actually suspended execution when pressed during normal operation, we are removing it for now. The button can be reintroduced once we have support for truly pausing the program while it is running.

Changes

• Remove pause button from GUI and related code.
• Restore writing of the route checkpoint file when the program is terminated.

TODO:

• Determine the correct is_flat option for the route checkpoint from router options.
• Update the pictures/docs for graphics.