Better USFM versification analysis

[Enkidu93]

Fixes #405
Partially fixes #416

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This change is 

[ddaspit]

@ddaspit partially reviewed 10 files and all commit messages, and made 4 comments.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on Enkidu93).

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src/SIL.Machine/Corpora/UsfmVersificationAnalyzer.cs line 16 at r1 (raw file):

    }

    public class UsfmVersificationDiagnostic

Can we make this class immutable, or, at least, immutable externally?

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src/SIL.Machine/Corpora/UsfmVersificationAnalyzer.cs line 69 at r1 (raw file):

    }

    public class UsfmVersificationAnalyzer : UsfmParserHandlerBase

I would rename this to UsfmVersificationAnalyzerHandler. I got it confused with the UsfmVersificationAnalyzerBase class.

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src/SIL.Machine/Corpora/UsfmVersificationAnalyzerBase.cs line 25 at r1 (raw file):

        public UsfmVersificationAnalysis AnalyzeUsfmVersification(
            HashSet<string> books,

I would rename this to bookIds to differentiate it from the other overloaded method.

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src/SIL.Machine/Corpora/UsfmVersificationAnalyzerBase.cs line 36 at r1 (raw file):

        public UsfmVersificationAnalysis AnalyzeUsfmVersification(
            HashSet<int> books,

I would rename this to bookNums.