Remove redundant semicolons.
Refactor named resource management code.

- In preparation for the explicitly typed actuators interface, code for managing
  named resources has been refactored into a separate class. This code consists
  of convenience methods wrapping a std::map container, and occur often enough
  that factoring it out to prevent duplication makes sense.

- Code that is not part of the public API, and hence with no stability guarantees
  has been moved to the internal folder/namespace. It only affects the named
  resource management and symbol demanglind methods so far.
Add explicit actuator hardware interfaces.

- These classes are similar to the existing joint equivalents, and are useful
  in setups leveraging the transmission_interface.