Improve feedback

[vvasco]

This PR improves the feedback provided to the user, assigning a score based on the following considerations:

• if the test is completed in < 10s, the user is assigned with a high score;
• if the test is completed in > 10s and < 20s, the user is assigned with a medium score;
• if the test is completed in > 20s, the user is associated with a low score.

Note: these values are adopted by physiotherapists to evaluate the risk for falling of the subject.

For computing the score, we rely on the walking speed estimated while performing the test, instead of the time. This allows us to produce a low score if the person stops moving or if moving slowly. In any case, if the line is not crossed, the test is considered failed.

The PR also introduces the getState service, which provides information about the result of the motion analysis, as:

• the exercise / test being performed and the related parameters;
• the state of the user (if standing, sitting or has crossed the line for the TUG);
• the result of the analysis (step length, width, speed).

[vvasco]

This situation is handled in 2601d75. When the user stops walking to ask questions, a new score is not assigned (the last computed score is considered to provide a feedback).