additional refactoring and improvements

This is 95% complete and I don't see any major issues.
.targets files are now imported
improved condition expression parser and now use it for expressions in properties
treat properties and metadata separately
better ordering of imports and emulation of missing system files
added debug message collecting (needs integration with cppcheck debug messages)
support for nested and chained properties
support for ARM and ARM64 platforms (needs integration with cppcheck)
import Directory.Project.props and Directory.Build.props when found

Author: IOBYTE