ZODB Components: erp5_simulation: Migrate Solvers and Testers from filesystem (MR !1093).

This moves portal_solver_processes from erp5_base to erp5_simulation as its
Portal Type definition is already there and it was initially moved away from
erp5_simulation presumably because erp5_simulation was for new Simulation at
that time.

Also, as delivery_causality_workflow uses portal_solver_processes, move it to
erp5_simulation (along with delivery_causality_interaction). This required
fixing Unit Tests to install erp5_simulation before erp5_trade (it already
depended on it anyway).