update size of enemyprefabs array
Add difficulty levels to New Game screen
Merge remote-tracking branch 'origin/develop' into develop

Conflicts:
	Assets/Scripts/BossShootInterval.cs.meta
	Assets/Scripts/boss_scripts/Boss1_moveV2.cs.meta
	Assets/Scripts/boss_scripts/BossProjectile_V1.cs
	Assets/Scripts/boss_scripts/BossProjectile_V1.cs.meta
	Assets/Textures/buttons.meta
Update Play button to launch New Game screen

The Play button on the Main Menu now loads the New Game screen when
clicked
Add a corkboard to pause menu background and note paper for resume button
Merge branch 'develop' of https://github.com/GGProductions/LetterStorm into develop
Remove unneeded meta file
Add Quit Game button and better positioning of pause menu buttons
Add How To Play button, more positioning
Enhance data saved

The PlayerData object was updated to include more properties to use to
save game data.
Finish look and some implementation of Pause Menu
Edit pause menu buttons, add first page of How To Play menu
Add Pause Menu resizing based on screen size of game
Integrate New Game screen with game

The difficulty level and lesson chosen on the new game screen are now
available within the game.   The Manage Lessons screen has a title.
Assign title image to Manage Lessons screen

Sorry, this got left out of the last commit somehow...
HUD update
Fix bug #2 in which Game is paused upon second load
Fix bug #1 in which background freezes after going to main menu from the pause menu
Merge branch 'develop'