Implement costs charged after death or for the full period (alive and dead)

These types of costs are relevant e.g. for term fixe insurances and for premium waiver riders upon death.

Implementation works by adding a "AfterDeath" and "FullContract" value to the cost frequencies, and a fourth dimension ("survival","guaranteed","after.death") to the internal cost cash flow array.

This additional dimension is kept in all cost cash flows and present values (PV could be summed!). But the abs present values and all premium compositions, reserves etc. are not influenced.

Export to excel adds several new columns in the CF and PV tabs.

Implements the feature request #61