Stop Bob when fire is pressed & volume adjustment

* BobController.java
- moved code to check the state of fire key ahead of movement keys to
stop Bob as soon as fire key is pressed

* Modified Assets:
- increased volume of sound effect when ball hits an object
(ball-hit.wav)
- increased volume of sound effect when enemy dies (justin-die.wav)
Optimized Bob's movement with accelerometer & bug fix

* BobController.java
- refactored MAX_VEL to MAXIMUM_VELOCITY
- added getter method for returning maximum velocity
- modified signature of update method to receive the maximum velocity
for Bob
- replaced constant MAX_VEL with the received maxVelocity value

* GameScreen.java
- added two threshold values instead of one for determining when to
start moving Bob and when Bob should attain maximum velocity
- updated parameters for controller.update() method
- refactored processAccelerometerInput() method to
getMaxVelocityFromAccelerometerInput() and changed its return type to
float
- [BUG Fix] stop accelerometer processing when Bob is in dying state to
prevent switching of directions during death animation
- added calculation for slow movement when accelerometer values are
within the two thresholds