Added sobol initial design

[apaleyes]

Issue #, if available: #278

Description of changes: Follow up on #280 . Fixed issues with optional dependencies for Latin and Sobol designs.

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Codecov Report

Merging #283 into master will decrease coverage by <.01%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #283      +/-   ##
==========================================
- Coverage   89.78%   89.77%   -0.01%     
==========================================
  Files         118      119       +1     
  Lines        3818     3835      +17     
  Branches      427      427              
==========================================
+ Hits         3428     3443      +15     
- Misses        309      311       +2     
  Partials       81       81

Impacted Files	Coverage Δ
emukit/core/initial_designs/base.py	85.71% <ø> (ø)	:arrow_up:
emukit/core/initial_designs/__init__.py	100% <ø> (ø)	:arrow_up:
emukit/core/initial_designs/random_design.py	100% <ø> (ø)	:arrow_up:
emukit/core/initial_designs/latin_design.py	90% <ø> (ø)	:arrow_up:
emukit/core/initial_designs/sobol_design.py	88.88% <88.88%> (ø)

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[apaleyes]

Thanks! You would it need to push this now though, I can't do it anymore