add query manager

[ajshedivy]

Fixes #

• add query manager for better API usage:

# connection logic
job = SQLJob()
job.connect(creds)

# Query Manager
query_manager = QueryManager(job)

# create a unique query
query = query_manager.create_query("select * from sample.employee")

# run query
result = query_manager.run_query(query)

job.close()

---

with SQLJob(creds) as job:
    query_manager = QueryManager(job)
    query = query_manager.create_query('select * from sample.employee')
    result = query_manager.run_query(query, rows_to_fetch=5)

with SQLJob(creds) as job:
    query_manager = QueryManager(job)
    result = query_manager.query_and_run('select * from sample.employee', rows_to_fetch=5)

Changes proposed in this pull request:

-

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• [ ] If this PR fixes a bug, I've added a test that will fail without my fix.
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