Minor update v0.6.1.5.1

You might have noticed a series of updates since the first v0.6.1.5 update drop. The changes were minor and only applied to user content and level editor only. But since many of you were asking about the changes, here's the complete list:

• Flat custom sprites rotation not working
  
• Custom sprites do not appear in the user adventure when you play the levels from the browser
  
• Custom-defined sprites showing invalid sprites in the level editor