Added the top and bottom keybindings.

Also, moved everything to a dictionary, to avoid endless if-else
ladders.
Add STOP button. Bound with Space key.

Pressing the space key will kill all the thrusters.

The vehicle will come to a rest after it loses its inertia.
Add the actions for STOP button.
Added the keyboard shortcuts in the button text.
Merge pull request #37 from icyflame/keyboard-control

Keyboard Control: Improvement
Remove the kraken_visualtization dependency.

As per suggestion by @prudhvid at https://github.com/iit-kgp-auv-team/kraken_3.0/issues/38
Add subscriber in the keyboard_control python file.
Complete showing values of the force in the Python GUI
Updated force change for yaw to +/- 0.5
Merge pull request #39 from icyflame/keyboard-control

Keyboard Control: Show values of the force in the Python GUI