Mara-db

- Add new parameters delimiter_char and csv_format to all copy command functions (allows for better quoting JSONS, arrays, strings with tabs)
- Add warnings for unused parameters
- Make code a bit more pep-8 compliant

**required-changes**

- Adapt own implementations of `copy_to_stdout_command`, `copy_from_stdin_command` & `copy_command` (add the two new parameters).
- Test whether everything still works (has been working reliably in three big projects for 4 weeks now)

- Revert commit [422c332](https://github.com/mara/mara-db/commit/422c332b09b4e28e19289f0baa27f5102ade9a03) (Fix pg to pg copy command for json data). It was causing too much trouble.

- Allow MARA_AUTOMIGRATE_SQLALCHEMY_MODELS to be a function (in order to improve import speed)
- Change MARA_XXX variables to functions to delay importing of imports
- Fix pg to pg copy command for json data
- Move some imports into the functions that use them in order to improve loading speed
- Remove dependency_links from setup.py to regain compatibility with recent pip versions

**required changes**

- Update `mara-app` to `>=2.0.0`

- Add oracle db access
- Add SSL standard parameters to PostgreSQL connection string
- Add missing footer parameter to Oracle copy to stdout command
- Change arguments for sqsh client to return non zero exitcode in error case
- Add single quotes around PostgreSQL passwords to prevent bash errors when the password contains certain characters

- Make graphviz engine in schema visualization selectable
- Implement Redshift DB
- Show enums in schema drawing for constrained tables
- Extend copy_to_stdout_command with "footer" argument for PostgreSQL DB

- Move sqlalchemy auto-migration from mara-app to mara-db
- Remove `config.mara_db_alias` function
- Move function `sqlalchemy.postgres_cursor_context` to module `postgresql`
- Remove `sqlalchemy/session_context` context handler
- Import graphviz only when needed
- Update / improve documentation
- Add port to sqlalchemy postgres connection string
- Extend copy_to_stdout_command with "header" argument

**required changes**

- Replace all occurrences of `mara_db.config.mara_db_alias()` with `'mara'`
- Replace `mara_db.sqlalchemy.postgres_cursor_context` with `mara_db.postgresql.postgres_cursor_context`
- Change all usages of `mara_db.sqlalchemy.session_context` to psycopg2 using `mara_db.postgresql.postgres_cursor_context`