Created upgraded sprites for the Slower

-Changed the first upgraded sprite to the last one to match the color schemes of the Archer (Blue = Lvl 1, Red = Lvl 2, Whitish = Lvl3)
-Modified PlayerHelpers' pseudo-random behavior:
  -Added a random range to slighly alter how often they attack
  -Added a single Random instance to avoid them all using the same random seed and always targetting the same enemies at the same times
-Made the Slowers appear on the top part of the player fort sprite
Updated the Level Background

-Removed the mistakes with the arcs on the right side and bottom of the flowers, which cut into the pistil of the flowers
-Scaled the flowers down 60% so they're not as large as the enemies
-Kept the old background but renamed it Level Background Old
Started Creating the How To Play Tutorial

- Made the first two screens of the How to Play tutorial
- Added a new game state: HowToPlay
- Added a new HowToPlayScreen Grid on GamePage.xaml
- Added a new HowToPlayScreen screen to ScreenManager
- Took the standing sprite for the Goblin, Armored Goblin, and Flying Goblin, and made them each a separate asset so they can be used in XAML
- Changed the icon for the Invincibility item in the shop to the Invincibility icon instead of the Fortify Walls icon
Created a graphic for the Game Over Screen

-Changed the Archer and Slower's MaxLevels from 4 to 2
-Made Archers able to attack different types of enemies as they leveled up
-Added a KingGoblin sprite that is only used in the Game Over screen
-Modified the Level Background so the strokes scaled with the flowers and moved the art board up 1 pixel, eliminating a black line on the bottom of the image and revealing the top of the leftmost mountain, which was previously cut off
Merge branch 'GameOverGraphic' into StartCreateHowToPlay
Merge branch 'StartCreateHowToPlay'