Added self tests capabilities to the Shadow Hand.

There are just a few tests and I need to add more of them (https://app.asana.com/0/1070189390521/3894963262823) but this is the base for the self tests (automatic diagnostic of the hand). The tests we run here are:
 * check if some services are there (correct initialisation of the hand - probably not necessary but here for STIFF FLOP as well)
 * check the mse for different fingers using sr_movements. The mse threshold is quite low meaning the test fails for some of the fingers. Will be adjusted later when we run it on the real hand.

To test it, you can use the gui plugin for self tests (not yet merged https://github.com/shadow-robot/sr-visualization/pull/2)