The reviewboard build backend writes out a package-dependencies.txt file

as part of most operations. This was including package_only_dependencies

all the time, which cause editable installs to fail now that the

rbintegrations dependency has been bumped to an unreleased dev version.

This change makes it so when we write out the dependencies file, we only

include those if we're building a wheel or sdist.
While in here, I fixed a couple small doc and syntax issues and added

_write_dependencies() calls to a few additional methods, in case the

build backend ends up calling them in isolation without first calling

some of the other methods.

Did an editable install and saw that it worked.