add minor physics brick changes for CAT-1112, CAT-1113 and CAT-1115
reorder physics bricks in category
rename collision with brick
fix bug in gravity and velocity brick
Merge pull request #1088 from Catrobat/physics_minorBrickChanges

add minor physics brick changes for CAT-1112, CAT-1113 and CAT-1115
CAT-1116 #done physics glide to behaviour