Remove usage of get_ordered_interfaces but update parameter validation instead

[christophfroehlich]

Fixes #116

• admittance_controller: There were some copies of the interface names without ever using them again.
• forward_command_controller: I changed the joint and interface parameters to be read_only, then we don't need the ordering there at all. This might be a breaking change, but I don't think that dynamically changing that would have worked without notifying the CM?

[codecov]

Codecov Report

❌ Patch coverage is 98.85057% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.91%. Comparing base (228c586) to head (929543f).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
..._controllers/src/joint_group_effort_controller.cpp	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1816      +/-   ##
==========================================
- Coverage   86.07%   85.91%   -0.16%     
==========================================
  Files         133      133              
  Lines       13282    13149     -133     
  Branches     1153     1146       -7     
==========================================
- Hits        11432    11297     -135     
- Misses       1478     1480       +2     
  Partials      372      372              

Flag	Coverage Δ
unittests	85.91% <98.85%> (-0.16%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...dmittance_controller/src/admittance_controller.cpp	75.08% <ø> (+0.33%)	⬆️
...ollers/test/test_joint_group_effort_controller.cpp	98.00% <100.00%> (-0.44%)	⬇️
...s/test/test_load_joint_group_effort_controller.cpp	100.00% <100.00%> (ø)
...ommand_controller/src/forward_controllers_base.cpp	80.35% <ø> (-5.13%)	⬇️
...ontroller/test/test_forward_command_controller.cpp	98.21% <100.00%> (-0.45%)	⬇️
...ller/test/test_load_forward_command_controller.cpp	100.00% <100.00%> (ø)
...oad_multi_interface_forward_command_controller.cpp	100.00% <100.00%> (ø)
...est_multi_interface_forward_command_controller.cpp	98.79% <100.00%> (-0.34%)	⬇️
...ontrollers/src/joint_group_position_controller.cpp	66.66% <100.00%> (+5.12%)	⬆️
...lers/test/test_joint_group_position_controller.cpp	97.91% <100.00%> (-0.45%)	⬇️
... and 5 more

... and 2 files with indirect coverage changes

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