Add instruction executor for high-level robot control

[urfeex]

With the trajectory point interface there is a method of executing motions with only the urcl present as shown in https://github.com/UniversalRobots/Universal_Robots_Client_Library/blob/master/examples/trajectory_point_interface.cpp

However, usage is a bit cumbersome, we might want to support a one-liner for executing ptp motions, instead.

This PR adds the InstructionExecutor, a high-level module that uses existing functionality to provide simple-to-use interfaces, currently to execute MoveJ, MoveL and sequences of the two. In future, we might extend that to other instructions such as other motion types, but possibly also other functionality, hence the more general name.

[codecov]

Codecov Report

Attention: Patch coverage is 98.82353% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.95%. Comparing base (2c12bee) to head (b9c2235).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/ur/instruction_executor.cpp	98.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #242      +/-   ##
==========================================
+ Coverage   71.71%   72.95%   +1.23%     
==========================================
  Files          71       75       +4     
  Lines        2786     2880      +94     
  Branches      353      360       +7     
==========================================
+ Hits         1998     2101     +103     
+ Misses        596      588       -8     
+ Partials      192      191       -1     

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