[Open Assets] SRB1 Remake 1.4

- Updated Great Unknown's Skybox to match more with the original.
- Springs were added to Ice Palace 1 and Echidnapolis 1 for the MP version thanks to TLKG.
- All the levels are now multiplayer compatible in both versions, also thanks to TLKG.
- Removed unused textures and organised the Maps folder.

Pretty excited to see this come out after the demands that I've received for it, the fact that you can now host a SRB1 Remake server with everyone being able to complete it is great and I couldn't thank TheLastKitchenGun more for that. Anyways hope you enjoy this update!
I can approve my own stuff now, hehe

- Added 2.1 Flickie sprites as well as some graphics touchups.
- Fixed the music and renamed all the lumps.
- Updated the Multiplayer version to only be a SOC. (Needs to be added after the mod)
- Updated the Remastered Music addon to match the current lumps.