Improve first run KDE neon user edition

On Fedora, or openSUSE, running kdesrc-build --initial-setup installs lots of dependencies, and you can (generally) successfully build KDE Frameworks in one go.

On KDE neon (currently interpreted as "Debian") you get a much, much smaller selection of build-dependencies installed, such that after kdesrc-build --initial-setup the very first not-ECM framework you get to is likely to fail to build. Introduce a "neon" section of packages, and fill it up at least enough to get through building dolphin. This makes the kdesrc-build experience much nicer: no longer do you need to trawl through build failure logs on KDE neon user edition to figure out what is missing, because it's already installed by the build tool (which knows about these dependencies on other platforms, just not on our flagship demonstration developer engagement OS).

While here, stick in some # comment lines, which are supported by _readPackages() but weren't used until now.