Certificate support + C_Encrypt and C_Decrypt support

Hi there,

I would like to propose the following two patches which I wrote. The first one adds certificate support to SoftHSM. The second one, is an implementation of the C_Encrypt and C_Decrypt operations. I used the C_Sign as a code base and adapted it. I discussed the possibility to add these functionnalities in v1 of softhsm with Rickard and I hope the code quality will be decent enough. Adding those two functionnalities would be great as there are essential to use the softtoken in other apps.

Best regards,

Thomas Calderon