Deprecate forward_command_controller specializations

[christophfroehlich]

In a recent PMC meeting we decided to deprecate the specializations for the sake of reducing duplicate code here in the repository.

Should we rename the package (can be done by adding a shim package with the old name and deprecation warnings) before adding another controller (twist_controller from #300)?

Slightly related to #157 (no need for controller specifications if we use standard Float64MultiArray message anyways)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.13%. Comparing base (f59b5a0) to head (4f9269c).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1913   +/-   ##
=======================================
  Coverage   85.13%   85.13%           
=======================================
  Files         144      144           
  Lines       13968    13968           
  Branches     1201     1201           
=======================================
  Hits        11891    11891           
  Misses       1670     1670           
  Partials      407      407           

Flag	Coverage Δ
unittests	85.13% <ø> (ø)

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

Files with missing lines	Coverage Δ
..._controllers/src/joint_group_effort_controller.cpp	62.50% <ø> (ø)
...ontrollers/src/joint_group_position_controller.cpp	66.66% <ø> (ø)
...ontrollers/src/joint_group_velocity_controller.cpp	62.50% <ø> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[saikishor]

LGTM