* moves dolphin-specific settings out of Base.props
* creates exports.props for externals, allowing to easily import
individual Externals
* corrects some cruft that accumulated and probably contributed
to msbuild overbuilding
New dolphin-tool command: "header"
-b / --block_size
-c / --compression
-l / --compression_level
Informative RVZ/WIA header2 value "compression_level" is now a s32 instead of a u32, because negative compression is a thing.
Speaking of, it is now possible to use negative compression levels in dolphin-tool's convert command (not the GUI, though).
