Miscellaneous Win32 related changes

 * register maildir provider - it was built, but not registered, though
   it is required for evolution; there will be needed more changer, but
   let's have this as a	starter
 * write Windows full path in .service files - D-Bus requires a Windows
   full path there, not a Unix-like, thus depends on WIN32_SERVICELIBEXECDIR,
   which should provide this path with forward slashes
 * introduce e_util_win32_initialize(), which should be called at
   the beginning of the main(); it makes also sure that D-Bus daemon is running