Updated Tests, Tapping features and Vignettes

[itismeghasyam]

• The tests assume that Handle the case when no feature extraction functions or model list is passed #56 is merged, also I have forked this from Sagebio develop, so please overwrite the corresponding files in this pullreq, with the ones changed in Handle the case when no feature extraction functions or model list is passed #56
• A minor issue with GuanLab model, reported as features output of guanlab_model(), are 1s or 0s #57

[itismeghasyam]

• Tests updated
• tapping_features moved from sensors to get_tapping_features, and is now un-exposed. As tapping features are not generalized to models like accel and gyro. resolves Redundant tapping features functionality #61
• sensors vignette updated to reflect new input parameter structure to *_features (overlap removed)