fixing minor issues flagged by checkstyle

largest change is the refactoring of Lease#assign(...) to call some helper methods, limiting method length <=30 lines.
refactoring IndexationService#indexate (checkstyle flags method is too long)

scoping local variables more tightly, make final if not reassigned, identify the 4 bigdecimals constituting the result of the indexation calculation.
refactoring IndexationService#indexate (checkstyle flags method is too long)

introduce concept of an IndexationResult, and use this to apply changes to the Indexable input.
refactoring IndexationService#indexate (checkstyle flags method is too long)

scope local vars more tightly into the if block, make final where poss.
refactoring IndexationService#indexate (checkstyle flags method is too long)

factor out new 'indexateToResult' method.
refactoring IndexationService#indexate (checkstyle flags method is too long)

simplify the 'indexateToResult' method, exit early if no index with the input Indexable.
refactoring IndexationService#indexate (checkstyle flags method is too long)

factored out new indexateWithIndexToResult when the input does have a non-null Index.