Finished bottom action buttons

UI Update:

- 2 new buttons added to the bottom actions list. These are the Repair button (to repair turrets and buildings, except the main tower) and the Reload button to reload ammunition in the turrets. They also change the cursor for easier understandability of the current function in place.

Gameplay update:

- Health bars now properly appear and disappear when a turret or a building takes damage or when the user repairs them.