VirtualBox 5.1.0 Beta 1

# The following major new features were added:
* VMM: new APIC and I/O APIC implementations that result in significantly improved per-formance in certain situations.
* VMM: added support for Hyper-V paravirtualized debugging of Windows guests.
* VMM: emulate even more MMIO and shadow pagetable exits without going back to user mode.
* GUI: overall migration to Qt5.
* GUI: passive API event listener improving the VM GUI performance and response time.
* better support for Python 3 .
# In addition, the following items were fixed and/or added:
* VMM: many fixes.
* GUI: the Detach UI action is now a part of the VM Machine menu.
* GUI: reworked session information window.
* GUI: the new VM wizard now allows to choose the VM location for the VM which is being created.
* GUI: various bugfixes and internal cleanup.
* Storage: use fallocate or similar if present to speed up creating fixed-sized disk images.
* Storage: implemented NVMHCI-compatible storage controller.
* EFI: many improvements, for example allow to boot from USB.
* OVF: improved handling of signed manifests.
* Windows hosts: rework COM proxy.
* Linux installers: no longer rely on DKMS for module rebuilding.