cohesive element (continued)

- introduce a global clock module, with a global clock type
- glb_clock: time, dtime, kstep, kinc

- element isdv stores nstep and ninc to compare with glb kstep and kinc
- logical var. last_converged

- damage variables stored in ig point sdvs

-next: write ddsdde, write glb_clock, and scrutinize code