Rename master branch

[wtgee]

We're a bit behind on this, but I'll be renaming most of the master branches to main, following the general trend of the github community.

Need to rename branches, ensure master is not used in any automated build processes and if so change them, then make sure developers have necessary instructions for updating local environment (provided by github).

Should be pretty easy to do as long as we're not actually using master in automated builds.