Small Changes and Lag Reduction

When a lot of mobs died at once and a lot of coins were instantiated all at the same time, the game slowed to a crawl. To alleviate this, I implemented two fixes:

- Removed animation from the coins on the ground, as having a lot of AnimationPlayers running at once and constantly was contributing

- Created a Coin Pool, so that coins are only instantiated in the first minute or two of gameplay and stored far off screen with their physics processes, collision boxes and visibility turned off. Then, when a mob dies, it grabs an unused coin from the array of already instantiated coins and makes it visible, turns on collision boxes and moves it to where the mob died. The pool for coins is quite large, but there are backups in place so that if somehow all the coins in the pool are on the ground, the game will start instantiating new coins, just as a fail safe.

Other fixes and changes:

- increased the health of the boss

- made the boss's charge up animation more obvious

- added a blinking and growing and shrinking animation to the tnt before it explodes on the ground

- fixed the upgrades persisting through restarts

- lowered the health of tnt goblins slightly

- increased the run speed of the samurais

- slightly increased the size of the wizard's projectiles so they are easier to see

-  updated the upgrade store so that it scales to screen size properly (this was a huge headache, as it took me a minute to fully understand how the vbox, hbox, center, margin, panel etc etc containers worked and how to manipulate them properly to where I wanted them on the screen, holyyyyyy)

- updated some of the UI so it scales properly (still one or two things that I need to fix, but it is late right now

- added screen shake and a redness to the outer part of the screen when the player gets damaged, both of which intensify if the player gets continually damaged in quick succession.

- added remappable controls in the pause menu (menu opened with TAB; not the upgrade store menu). These controls DO persist through restarts, but DO NOT persist if you close and re-open the game (was having issues with the config files working properly).

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