current build doesn't build only monodevelop and addins,
but also a lot of subprojects

this makes the process error-prone and complicated.

the suggestion:
a Main.sln only for building / working on monodevelop
a MainDev.sln integrated with all subprojects (as now), not always able to build, if work is done on subprojects.

the idea is to build this subprojects with CI in their own dotdevelop-repos
and consume them in the build process of Main.sln.