win32: Use version information from configure.ac to populate the Windows-specific files that need it - config-win32.h, version.txt, hexchat.rc, hexchat.iss

This is done via T4 templates. The original files are now generated at build-time and so have been added to .gitignore and removed from the repository, with the exception of version.txt which must be hosted on GitHub for the updater plugin.