namelist parameter to set maximum liquidus temperature

[eclare108213]

• Short (1 sentence) summary of your PR:
  Add a namelist parameter in place of the currently hardcoded maximum liquidus temperature
• Developer(s):
  @eclare108213
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Icepack testing is currently broken on my laptop due an iOS bug that prevents diagnostic files from closing properly, awaiting fixes from the consortium repo. Spot checks show the diagnostic output is BFB.
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • Yes
  • No but the namelist parameter should be added to CICE also
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please provide any additional information or relevant details below:

The current default value in CICE and Icepack is Tliquidus_max = -0.1, the reason for which is a mystery. This limiting (in add_new_ice) has been removed completely in the E3SM column physics, which did affect the solution substantially. (It also occurs in the FSD code, which is not yet available in E3SM.) With this PR, the limiting value can be set to anything; in particular, Tliquidus_max=0. should work. Since -0.1 is arbitrary, the official default value is set to 0. in the code but it is -0.1 in the baseline namelist (icepack_in) for backwards compatibility; this should probably be changed to 0.0 once sufficient testing of its impacts has been done in coupled systems. Addresses CICE-Consortium#385.