Added branch support to the dimension list system. This means that you can now have one repository (for example, IrisDimensions/overworld) with multiple branches of separate dimensions! (For example, overworld-legacy is on the IrisDimensions/overworld repository under branch "legacy".) With this update, you can now do /iris download overworld-legacy
Added error message if a branch is not specified on the listing or if it couldn't be found