Fix automatic mouse grabbing/releasing when running as a vmware guest.
1. The xf86inputvmmouse is not loaded by default. Add it.
2. InptutDevice sections for which specify a driver are ignored if
AutoAddDevices is enabled (which it is by default). See [1]. Instead use
an InputClass to load the vmmouse driver.
[1] https://www.x.org/archive/X11R7.7/doc/man/man5/xorg.conf.5.xhtml#heading8
