Standardize parameter parsing

[AndyZe]

Particularly, moveit_servo/src/servo_parameters.cpp should be standardized.

I think it's a good idea to ignore int's getting cast as doubles, but throw a warning if the parameter type does not match expected otherwise.

[henningkayser]

@AndyZe thanks for filing this. I was actually about do create a similar issue to finally get #313 going. For handling parameters, @tylerjw and I have already started discussing some design ideas for a generic config API that could be applied to MoveIt or other ROS 2 packages.

[aaroosh-07]

can i take up this issue

[henningkayser]

This issue has become obsolete with the efforts being implemented with #335. The Servo refactoring in particular has its own issue that builds on top of param refactoring: #917. I'm closing this.