Refactor sample result

[jvanhoefer]

The sample result was never used, while the McmcPtResult did not ensure a stable interface to the outside world. Fixed that. Might not be the final solution to the problem, but should definitely be an improvement

[codecov-commenter]

Codecov Report

Merging #804 (de013ac) into develop (4c6e013) will increase coverage by 33.90%. The diff coverage is 92.68%.

@@             Coverage Diff              @@
##           develop     #804       +/-   ##
============================================
+ Coverage    51.93%   85.83%   +33.90%     
============================================
  Files          106      106               
  Lines         7560     7574       +14     
============================================
+ Hits          3926     6501     +2575     
+ Misses        3634     1073     -2561     

Impacted Files	Coverage Δ
pypesto/__init__.py	100.00% <ø> (ø)
pypesto/objective/history.py	96.00% <ø> (+50.24%)	:arrow_up:
pypesto/store/read_from_hdf5.py	91.26% <ø> (+35.71%)	:arrow_up:
pypesto/result/sample.py	84.00% <91.66%> (+56.22%)	:arrow_up:
pypesto/result/__init__.py	100.00% <100.00%> (ø)
pypesto/result/result.py	100.00% <100.00%> (ø)
pypesto/store/save_to_hdf5.py	96.82% <100.00%> (+24.60%)	:arrow_up:
pypesto/optimize/optimizer.py	50.32% <0.00%> (-39.31%)	:arrow_down:
pypesto/optimize/task.py	92.30% <0.00%> (-7.70%)	:arrow_down:
pypesto/objective/amici_util.py	82.53% <0.00%> (-1.59%)	:arrow_down:
... and 63 more

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[yannikschaelte]

@jvanhoefer what's the status here?