Eng 4291 Statement-level XML refactoring (See summary in this pull request comment).

In AbstractParsedStmt:
    Merged various classes' parse*Column(s) and parseCondition(s) functions into parseTargetColumns and parseCondition .

In the corresponding hsql Statement*.java code:
    Renamed voltGetXML to voltGetStatementXML wherever it applies to statements.

    Merge various classes' voltGetStatementXML, voltAppend*Columns, voltAppend*Condition(s), voltAppendParameters functions and inline code into
        voltGetStatementXML, voltAppendTargetColumns, voltAppendCondition, voltAppendParameters, and voltAppendChildScans functions
        in the most general applicable base class for each.

In voltGetStatementXML:
    Avoided use of "unknown" as a temporary VoltXMLElement name that never really survives. Emphasize structural commonalities/differences in the different DML statements.

Some small tweaks to the voltXML interface:
 -- target columns for update/insert were simplified to not redundantly name the target table.
 -- range variable indexEndExpressions properly append themselves to conditions (This is a fixed typo that is probably specific to explicit join syntax -- currently dormant code and still a little suspect).