Camera: Higher frequency limit for view/hand bobbing and footsteps

Rebased and tuned version of Calinou's original pull request.

'm_view_bobbing_speed' controls the frequency of view bobbing,
hand bobbing and footsteps, it was limited to a maximum of 40 (walking
frequency) so did not increase if player speed was modified by a
'speed buff', a sprinting mod or modified in .conf or advanced
settngs.

This commit raises the limit to 70 which is suitable for sprinting.