Improve tower targeting

[sdiaz7]

Refining Tower Targeting Behavior:

• Towers target nearest target, and update their priorities if an enemy is getting close to the player's base
• Projectiles are shot from the turret's cannon, or equivalent
• Automatic target switching when current target is out of range or killed

Definition of Done

• All description bullet points are satisfied
• Turrets correctly update their target
• Projectiles travel in the air and not through the ground

Initial Estimate: 4 Hours

[Nerucius]

Opened branch dev_Issue162 with 1 new commit.

Commit 3503886da8b9dd03f361f3a38f9383c0533d7159

• Turrets now target smoothly
• Turrets target the nearest enemy, not just the first one in range
• Turret range decreased to 35 from 200
• Bug Projectiles despawn inmediately after spawining

Estimated Time Left: 3

[Nerucius]

Commits on branch dev_Issue162:

• New Prefab structure for towers
• Projectiles now coming from tower muzzle
• Enemy Prefab restructured, Collider is now contained on the root GameObject instead of in the Mesh

Pull Request at #180

Issue is done. Final time 6 hours

[Nerucius]

Merged at #180