Remove all outdated, unmaintained project files and some unused dirs, and other stuff related to outdated build methods.
Originally committed to SVN as r2821.
* The most important project properties (especially paths) are now stored in VSProps files in generalised ways.
* Projects share VSProps files so they place output files in same locations and thus agree on where to find them.
* Avoid inconsistencies between build configurations/platforms as has happened often before.
* Now distributable binaries (aegisub.exe and aegisub-auto3.dll) will be placed in $(SolutionDir)/bin/, static libraries under $(SolutionDir)/lib/ and object files etc. under $(SolutionDir)/build/. Note that those locations are controlled by where the solution file is placed in the file system.
* libauto3 is no longer pulled in by a #pragma in auto4_auto3.c, but must instead be pulled in by making the aegisub project depend on the auto3 project, which must in turn depend on the lua50 project.
* Final binary filenames are now somewhat different. You get aegisub32.exe, aegisub64d.exe, aegisub-auto3lib32d.dll and more.
* There's still more that can be factored out, things like optimisation flags and defines.
Originally committed to SVN as r2819.
