Breaking changes: Rearrange "extras", MySQL support, remove deprecated args, sqlalchemy-redshift workaround

Breaking changes:

• Separate out "extras" in setup.py to avoid installing unnecessary dependencies - #38
  • You will need to change how you run pip install to get all of the dependencies you need. Please see INSTALL.md for the new things to add and alter any pip install records-mover calls accordingly.
• Remove deprecated and unused parameters in DataFrame source factory method - #44
  • Please remove schema_name, table_name and db_engine parameters to sources.dataframe() calls.

New features:

• Initial MySQL support - including importing and exporting of small amounts of data using INSERT and SELECT for now - #31

Bug fixes / reliability improvements:

• Work around sqlalchemy-redshift/sqlalchemy-redshift#195
• Redact known secrets from logging - #36
• Error message improvement to help find error details in stl_load_errors - #45
• Fix deprecation warnings from sqlalchemy-redshift and google-cloud-bigquery #44

Other updates:

• Improvements to database-driver internal integration testing and documentation - #31