Front-end support for LIMIT ROWS DELETE statements

The first commit you have already seen here on GitHub.  The second completes the ticket by doing error checking, planning the statement, and logging the explained plan:
* The HSQL parser stores the text of the DELETE statement in the VoltXML that it generates
* `DDLCompiler` generates VoltXML from the text of the DELETE statement to verify that the statement is a DELETE that targets the correct table
  * The statement is then saved in the catalog as a child of the Table 
* After `VoltCompiler` compiles stored procedures, it proceeds to compile any DELETE statements designed to help enforce the ROW LIMIT constraint
  * It's at this time that the explained plan is logged.
If you look near the beginning of this method, the call to `ddlcompiler.compileToCatalog(db)` is what actually (eventually) validates the DELETE statement (producing the XML that gets thrown away).  The ROW LIMIT number is also validated here, so it seems right to validate them together, and it also seems like a good place in general to put validation that we can't do in HSQL.

This is followed by a loop that updates the catalog with partitioning info for each table.  A comment indicates that this must be done before compiling procedures.  (Perhaps in our case it *might* be okay to compile the DELETE statement before this since we are forcing single-partition execution, but it would seem to be bad form--I like that we populate the catalog as much as possible *first*, and then proceed to do statement planning.)

So, I'd rather not try to compile the DELETE statement as we're populating the catalog with tables in DDLCompiler.  After some thought, it would be feasible to avoid the redundant parsing:
* Validate the XML for the DELETE statement, and store the XML in a map owned by `VoltCompiler`
* Re-factor `StatementCompiler` and its callee, `QueryPlanner` to accept XML directly

Alternatively, we could use regular expressions to validate the DELETE statement, and not parse it at all in DDLCompiler.  I'm pretty soured on regular expressions after seeing sqlcmd though.

In the big picture, how horrible is it to parse the DELETE twice?  I don't think it's that bad, but maybe I'm just being "overly expedient."