install: Add install.bat

Add install.bat for Windows.

Signed-off-by: Asias He <asias@cloudius-systems.com>
vbox: Add Windows support

Note: VBoxManage.exe is not added to %path% by default. User need to add
it. Perhpas we can add it in capstan instead.

Example:
cmd.exe -> capstan run -p vbox vbox.vdi

Signed-off-by: Asias He <asias@cloudius-systems.com>