Planning: changes for follow algorithm. (1) make sure acceleration is < 0 when the adc is between the front car and follow fence; (2) only add follow reference point when the point is behind reference line; (3) added parameter follow_drag_distance to adjust following behavior.

Planning: fixed follow issue in qp_st_graph. The reference line of follow should only be set when time is within the boundary range.

* Planning: fixed bug when generate init speed profile.

* pnc_map: style changes in pnc_map/path.h/cc

* Planning: Added acceleration constraint in qp_st_spline_speed.

bugfix: fix reference guide line bug
add unit test

add dp_st_speed_config.pb.txt and st_boundary_config_file.pb.txt. enable QP_SPLINE_PATH_OPTIMIZER in conf.