Move all in-repo deps to aegisub/vendor

aegisub/Makefile

aegisub/Makefile.inc.in

aegisub/Makefile.target

aegisub/build/csrihelper/csrihelper.vcxproj

aegisub/build/hunspell/hunspell.vcxproj

aegisub/build/hunspell/hunspell.vcxproj.filters

aegisub/build/libiconv/libiconv.vcxproj

aegisub/build/paths.props

aegisub/build/universalchardet/universalchardet.vcxproj

aegisub/libaegisub/common/charset.cpp

aegisub/tests/Makefile

aegisub/vendor/csri/Doxyfile

aegisub/vendor/csri/LICENSE

aegisub/vendor/csri/Makefile.am

aegisub/vendor/csri/ac/Makefile.am

aegisub/vendor/csri/acinclude.m4

aegisub/vendor/csri/backends/Makefile.am

aegisub/vendor/csri/backends/libass/Makefile.am

aegisub/vendor/csri/backends/libass/libass_csri.c

aegisub/vendor/csri/bootstrap