Rename to material and damage id

[PeriHub]

It should look like that:

 Physics:
    Material Models:
      Mat_1:
        Material Type: "PD Solid Elastic"
  Blocks:
    block_1:
      Material Id: "Mat_1"

[JTHesse]

Up for discussion, should we stick with Material Model and Damage Model or rename to Material Id and Damage Id @CWillberg

[CWillberg]

Its fine for me.