Simplify poromechanics initialization setup

[paveltomin]

Simplify definition of poromechanics initialization in the input file.

Instead of:

    <SoloEvent
      name="multiphasePoroelasticityPreEquilibrationStep"
      targetTime="-1e11"
      beginTime="-1e11"
      target="/Tasks/multiphasePoroelasticityPreEquilibrationStep"/>

    <PeriodicEvent
      name="solverApplicationsEquilibration"
      beginTime="-1e11"
      endTime="0"
      maxEventDt="1e11"
      target="/Solvers/reservoirSystem"/>

    <SoloEvent
      name="multiphasePoroelasticityPostEquilibrationStep"
      targetTime="0"
      target="/Tasks/multiphasePoroelasticityPostEquilibrationStep"/>

...

    <MultiphasePoromechanicsInitialization 
      logLevel="1"      
      name="multiphasePoroelasticityPreEquilibrationStep"
      performStressInitialization="1"
      poromechanicsSolverName="multiphasePoroelasticity"/>

    <MultiphasePoromechanicsInitialization 
      logLevel="1"      
      name="multiphasePoroelasticityPostEquilibrationStep"
      performStressInitialization="0"
      poromechanicsSolverName="multiphasePoroelasticity"/>

one now needs to specify only:

    <SoloEvent
      name="multiphasePoroelasticityEquilibrationStep"
      targetTime="-1e11"
      beginTime="-1e11"
      target="/Tasks/multiphasePoroelasticityEquilibrationStep"/>

...

    <MultiphasePoromechanicsInitialization 
      logLevel="1"      
      name="multiphasePoroelasticityEquilibrationStep"
      poromechanicsSolverName="multiphasePoroelasticity"/>

No results changes are expected.