Calibration creation date

[rettigl]

This PR:

• unifies the interface for calibrations, corrections and offsets, and their saving and loading.
• adds time-stamps for the creation of the respective correction, and displays them when loading (optional).
• adds Saving/loading procedures for momentum transformations/pose adjustments

closes #145
closes #149

[coveralls]

Pull Request Test Coverage Report for Build 7991449446

Details

• 597 of 652 (91.56%) changed or added relevant lines in 8 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.6%) to 91.137%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/calibrator/test_momentum.py	9	10	90.0%
sed/calibrator/delay.py	82	87	94.25%
sed/calibrator/energy.py	90	97	92.78%
sed/calibrator/momentum.py	108	115	93.91%
sed/core/processor.py	212	247	85.83%

Files with Coverage Reduction	New Missed Lines	%
sed/core/dfops.py	1	84.08%

Totals
Change from base Build 7963843656:	0.6%
Covered Lines:	5933
Relevant Lines:	6510

---

💛 - Coveralls

[rettigl]

This has grown relatively large again, but should be well covered by tests. @steinnymir please inspect the changed structure of the offset functions in energy and delay correctors (functionality should be the same and/or fixed according to docstring)