Do not take arbitrary arguments as configuration names

As a qbs newbie, I'm often typing commands like

qbs ? // trying to get help
qbs build help // trying to get help for build command
qbs qt-5-9-msvc-2015-64 // trying to build with profile "qt-5-9-msvc-2015-64"

In all of the above cases, qbs will interpret "?", "help", "qt-5-9-msvc-2015-64" as a configuration name, and will try to create build configurations with the same name, which is arguably unexpected.

We might therefore consider requiring configuration names to be qualified, e.g.

qbs qbs.configurationName:release

And show an error for all of the above commands.