Move the following out of ts_salobj into new package ts_utils:
- time functions such as current_tai
- angle functions such as angle_diff and angle_wrap_center
- test utilities such as modify_environ and assert_angles_almost_equal (rename from assertAnglesAlmostEqual)
Add trivial backward compatibility wrappers to ts_salobj that issues deprecation warnings and then call the new function in ts_utils.
Update ts_salobj to use the new versions (but continue to test the trivial backward compatibility wrappers).