devel/qbs: Resurrect port and update to 2.6.0

Qbs is a tool that helps simplify the build process for developing
projects across multiple platforms. Qbs can be used for any software
project, regardless of programming language, toolkit, or libraries used.

Qbs is an all-in-one tool that generates a build graph from a high-level
project description (like qmake or CMake) and additionally undertakes the
task of executing the commands in the low-level build graph (like make).