additional thermal crystal issues

[moellep]

After #6142 is released, the following issues remain:

• Take out "BELLA" from the example name
• Add a switch in Simulation tab to choose between analytic and simulated (fenics)
  (invoke fenics by using set_load(load_type) followed by solve_steady()/slow_solution() (depending on rep rate)
• Restrict simtype by rep rate:

if rep rate <= 1:
    only simulated solve is allowed
elif rep rate >= 100:
    either analytical or simulated solve are allowed