Also remedies places where the video backends and core rely on things
being indirectly included.

And rename it to VideoBackendBase because of conflicts within the backends itself.

Also gets rid of global headers

The new implementation has 3 options:
 SyncGpuMaxDistance
 SyncGpuMinDistance
 SyncGpuOverclock

The MaxDistance controlls how many CPU cycles the CPU is allowed to be in front
of the GPU. Too low values will slow down extremly, too high values are as
unsynchronized and half of the games will crash.
The -MinDistance (negative) set how many cycles the GPU is allowed to be in
front of the CPU. As we are used to emulate an infinitiv fast GPU, this may be
set to any high (negative) number.

The last parameter is to hack a faster (>1.0) or slower(<1.0) GPU. As we don't
emulate GPU timing very well (eg skip the timings of the pixel stage completely),
an overclock factor of ~0.5 is often much more accurate than 1.0

Yet another story of games loading weird shit into registers.

For some reason, Burnout 2 would (in rare situations) load invalid
addresses into cp_state.array_bases. What would the real hardware
do in this situation? Who knows, Burnout 2 doesn't actually enable
the vertex array with the invalid address so nothing kinky happens.

But dolphin tries to optimise things and starts using the address
as soon as it is loaded into memory. This causes GetPointer (which is
now much more vocal) to throw an error.

The Fix:  We don't call GetPointer until we are sure the vertex array
has been enabled.