Fix detection of plugin updates requiring newer Maven for building than

[kwin]

for running

Separate minimal Maven version detection for projects from requirements
of plugins
This closes #526

[stefanseifert]

thanks, looks good and solves the problem (i was bothered of it as well).

one remark: you removed the test class RequiredMavenVersionFinderTest completely. probably the test were not all valuable, but especially not covering all the complex parsing code in MinimalMavenBuildVersionFinder.processMavenVersionRange is bothering me - all those variants are not covered in the ITs.

[kwin]

probably the test were not all valuable, but especially not covering all the complex parsing code in MinimalMavenBuildVersionFinder.processMavenVersionRange is bothering me - all those variants are not covered in the ITs.

Most tests were not really useful as were mostly calls on mock objects, but the ones for parsing versions were indeed useful. Let me readd/extend those.