Refactor parameter links & optimization constraints

[rutgerfick]

• Refactors parameter links as classes or dictionaries that can be easily adapted to apply any parameter relationship.
• Is able to both link and remove a parameter (e.g. tortuosity), or link and replace a parameter with an differently parameterized parameter (optimization parameter, e.g. ODI for Watson distribution).
• Corrects fractional parameter to range from the minimum value of the target parameter to the maximum value, instead of 0 to maximum value.

closes #14
closes #28

[codecov-io]

Codecov Report

Merging #29 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
+ Coverage   81.86%   81.94%   +0.07%     
==========================================
  Files          61       61              
  Lines        5133     5133              
  Branches      579      579              
==========================================
+ Hits         4202     4206       +4     
+ Misses        774      770       -4     
  Partials      157      157

Impacted Files	Coverage Δ
dmipy/core/acquisition_scheme.py	72.61% <0%> (-0.6%)	⬇️
dmipy/distributions/tests/test_bingham.py	95.52% <0%> (+1.49%)	⬆️
dmipy/utils/tests/test_spherical_convolution.py	100% <0%> (+12.19%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ba3ab9b...39b5f74. Read the comment docs.

[coveralls]

Pull Request Test Coverage Report for Build 367

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.05%) to 82.526%

---

Files with Coverage Reduction	New Missed Lines	%
dmipy/utils/tests/test_spherical_convolution.py	1	95.35%
dmipy/data/saved_acquisition_schemes.py	2	83.33%
dmipy/data/saved_data.py	2	70.94%

Totals
Change from base Build 360:	0.05%
Covered Lines:	4355
Relevant Lines:	5133

---

💛 - Coveralls