Add builders for maint-0.3.0 branch
0.3.0 has now been forked off from the master branch onto a maint-0.3.0 and release-0.3.0 branch, per the usual protocol. It hasn't diverged much yet, but it's only a matter of time.
So, we should probably have maint-0.3.0 builders.
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information