Phase saving, restarts, and heuristic performance logs

[AntoniusW]

This is a preview PR adding two standard SAT/ASP techniques. Restarts in conjunction with the restricted guessing on applicable rules (in order to compute computation sequences as in other lazy-grounding ASP systems), however, have a negative impact on search performance. Unless further advances for lazy-grounding search to remedy that performance impact are available, this PR shall not be merged.

[codecov[bot]]

Codecov Report

Merging #202 (fcd2436) into master (21d074a) will increase coverage by 0.00%. The diff coverage is 70.64%.

@@            Coverage Diff             @@
##             master     #202    +/-   ##
==========================================
  Coverage     69.51%   69.51%            
- Complexity     2092     2159    +67     
==========================================
  Files           182      188     +6     
  Lines          8006     8261   +255     
  Branches       1416     1443    +27     
==========================================
+ Hits           5565     5743   +178     
- Misses         2086     2152    +66     
- Partials        355      366    +11     

Impacted Files	Coverage Δ
.../java/at/ac/tuwien/kr/alpha/commons/util/Util.java	9.09% <0.00%> (-0.29%)	:arrow_down:
.../at/ac/tuwien/kr/alpha/core/common/Assignment.java	86.66% <ø> (ø)
.../tuwien/kr/alpha/core/grounder/ChoiceRecorder.java	89.74% <0.00%> (+10.19%)	:arrow_up:
...ien/kr/alpha/core/solver/MixedRestartStrategy.java	0.00% <0.00%> (ø)
...olver/heuristics/AlphaHeadMustBeTrueHeuristic.java	0.00% <0.00%> (ø)
...ore/solver/heuristics/PhaseInitializerFactory.java	23.52% <23.52%> (ø)
.../ac/tuwien/kr/alpha/core/solver/DefaultSolver.java	64.84% <40.00%> (-1.22%)	:arrow_down:
.../tuwien/kr/alpha/core/solver/heuristics/VSIDS.java	91.48% <71.42%> (-0.18%)	:arrow_down:
.../tuwien/kr/alpha/app/config/CommandLineParser.java	82.26% <76.19%> (-0.63%)	:arrow_down:
...a/core/solver/heuristics/VSIDSWithPhaseSaving.java	76.92% <76.92%> (ø)
... and 19 more

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[rtaupe]

Now #239 pops up also here. We should really fix this issue ...

[rtaupe]

There is a bug: #255 (I don´t know if it is related to this pull request, but it occurs on this branch.)