Integration of tajo algebra module and SQL parser.

In the current implementation, QueryAnalyzer transforms a sql statement into a data structure that represents a parser tree and a query block. They has the following limitations:

• They can't support multiple block queries including table and scalar subqueries.
• They are tightly coupled to a certain grammar.

Before ASF incubation, I have developed tajo-algebra and tajo-frontend-sql. Tajo-algebra is a kind of intermediate layer. It represents a just relational algebraic expression. With this, we can do more interesting things. For example, we can enable users to describe a logical plan for a certain query. It also very helpful to support an another DSL.

For this work, tajo-algebra should be improved to support full specifications, and we should rewrite a SQL parser to use tajo-algebra.