LatinVerbClassifier#classification: refactor pseudo-case statement smell

Replace type checking and branching with
polymorphism.
wip
wip
wip
wip
Add guard clauses to DeponentStringDeriver
Change key for lookup calculation
migrate stem calculation out of prin parts extractor
rm dead methods
TypeEvaluator to use similar interface as other components
Move common interface using components
Formatting cleanup
Add comment to re: type v. classification
Extract methods on Stem Deriver
Extract method, simplify, use Forwardable in LatinVerbTypeEvaluator
Extract method, use Forwardable in Participler
Extract method, use Forwardable in Infinitivizer
Extract method, use Forwardable
Merge branch 'refactor-principal-parts-extractor' into nasty-refactor
Refactor TenseMethodApplicator

1.  Change implementation of `DefectiveChecker`:
prefer classes to module
1.  Extract `MutatorForVerbType` and
`TenseMethodsVectorizer`
1.  Simplify, cleanup, shorten, remove
boilerplate, etc.