Adding possibility for custon spice and spice kernel folders (Issue #716)

git-svn-id: file:///srv/svn/repos/tudat/trunk@543 ac7aa084-b6da-11df-bf42-7fac39f0224f
Ported BS beta code over from diverged branch.
Merge branch '034_BulirschStoer' of https://github.com/kartikkumar/tudat-svn-mirror into 034_BulirschStoer