Add support of the SKIP keyword

[ChunxuTang]

This PR

• adds support for the SKIP keyword of Cypher queries (translating SKIP to SQL OFFSET).
• aggregates the support of ORDER_BY, SKIP, and LIMIT in the query execution.
• updates planners accordingly.

Example query:

MATCH (p:Person) RETURN p.name, p.age ORDER BY p.age DESC SKIP 10 LIMIT 5

[beinan]

lgtm