change of `atTarget` handling

[kivel]

Current situation

The atTarget-flag of the axis is set to true even when the axis was stopped by a limit switch. Thus, not reaching the desired target.
Also, the setpoint is synced to the readback after ramping to standstill, which is not desired.

requested changes

• set atTarget only when the actual target is reached
• prevent setpoint from synching to actualPosition when stopped by limit switch.