[FEATURE] Read home position from SRDF in python scripts

[macmacal]

Description

Introduced in #79 ; instead of hard coding the home pose we should have one way to obtain all defined poses from the SRDF file.

References

• aegis_ros/aegis_moveit_config/config/aegis.srdf

  Line 33 in 1438d04

  <!--GROUP STATES: Purpose: Define a named state for a particular group, in terms of joint values in [rad] or [m].-->