Refactor model properties

[rutgerfick]

Refactors inheritance of spherical_mean, rotational_harmonics_representation and convolution_kernel_matrix to signal models into separate separate AnisotropicSignalModelProperties and IsotropicSignalModel classes.

Allows distributed models (watson- and bingham-distributed) to be used as convolution kernel.

[codecov-io]

Codecov Report

Merging #41 into master will decrease coverage by 0.16%. The diff coverage is 90.64%.

@@            Coverage Diff             @@
##           master      #41      +/-   ##
==========================================
- Coverage   82.35%   82.18%   -0.17%     
==========================================
  Files          61       62       +1     
  Lines        5253     5204      -49     
  Branches      614      612       -2     
==========================================
- Hits         4326     4277      -49     
- Misses        763      764       +1     
+ Partials      164      163       -1

Impacted Files	Coverage Δ
dmipy/utils/construct_observation_matrix.py	90.47% <ø> (ø)
...y/core/tests/test_raises_multicompartment_input.py	100% <ø> (ø)	:arrow_up:
dmipy/signal_models/cylinder_models.py	98.29% <100%> (-0.38%)	:arrow_down:
dmipy/optimizers_fod/csd_cvxpy.py	89.01% <100%> (+0.24%)	:arrow_up:
dmipy/core/modeling_framework.py	69.41% <100%> (-0.31%)	:arrow_down:
dmipy/signal_models/tissue_response_models.py	97.84% <100%> (+0.04%)	:arrow_up:
dmipy/signal_models/gaussian_models.py	98.27% <100%> (-0.34%)	:arrow_down:
...ils/tests/test_constructions_observation_matrix.py	100% <100%> (ø)
dmipy/signal_models/sphere_models.py	73.14% <100%> (+1%)	:arrow_up:
...ssue_response/tests/test_tissue_response_models.py	100% <100%> (ø)	:arrow_up:
... and 6 more

---

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 e1ba0bd...4911ca3. Read the comment docs.

[coveralls]

Pull Request Test Coverage Report for Build 460

• 126 of 139 (90.65%) changed or added relevant lines in 12 files are covered.
• 8 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.2%) to 82.876%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dmipy/core/signal_model_properties.py	43	46	93.48%
dmipy/distributions/distribute_models.py	14	24	58.33%
<!--	Total:	126	139	90.65%	-->

Files with Coverage Reduction	New Missed Lines	%
dmipy/utils/tests/test_spherical_convolution.py	1	100.0%
dmipy/data/saved_data.py	2	70.94%
dmipy/data/saved_acquisition_schemes.py	2	83.33%
dmipy/distributions/tests/test_bingham.py	3	93.15%
<!--	Total:	8		-->

Totals
Change from base Build 416:	-0.2%
Covered Lines:	4429
Relevant Lines:	5204

---

💛 - Coveralls