Introduce Database class abstracting MySQL access

[macbre]

• report list of tables
• report tables schema - columns, indices and stats
• allow to run EXPLAIN query
• take DSN-style URI as an argument (completed in #9):

from urlparse import urlparse

r = urlparse('mysql://alex:pwd@localhost/test')
print(r.username)
# 'alex'
print(r.password)
# 'pwd'

import MySQLdb
db=MySQLdb.connect(passwd="moonpie",db="thangs")

# ---

c=db.cursor()
max_price=5
c.execute("""SELECT spam, eggs, sausage FROM breakfast
          WHERE price < %s""", (max_price,))

# ---

>>> c.fetchone()
(3L, 2L, 0L)

• https://dev.mysql.com/doc/connector-python/en/connector-python-example-connecting.html
• https://github.com/PyMySQL/mysqlclient-python
• https://mysqlclient.readthedocs.io/user_guide.html#connection-objects