Fix animation import on non-bvh armature

The animation import only worked on bvh compatible armatures so far.
It is now fixed to work with nonbvh armature although it is still using
the name to find the correspondence between bones which is less than ideal.

Also reseting the camera around the armature bounds in the frame selector
so the whole armature is captured every frame.
ENH: Add initial rotation parameter to bvh reader

BVH files use Y as up whereas Bender uses Z as up. To prevent the armature
from being misaligned, we add the initial rotation parameter that allows
to transform the bvh armature in the Bender coordinate system.

The different poses  are modified according the initial rotation as to
preserve the animation but on the rotated armature. By default, the
initial rotation will transform a bvh armature in the Bender
coordinates.

The initial rotation parameter should ideally be set before reading an
armature from file. Setting it after will cause the reader to re-read the
file as it needs to recompute the rest and poses of the armature given the
new initial rotation.

This allows us to remove the fix code in the animation import to align
the animation armature and the target armature as they are now closely
aligned (unless the animation armature's pose is intended otherwise).
WIP