Mara-etl-tools

- Adapt to renaming of `data-integration` package to `mara-pipelines`.

**required changes**

- Requires `mara-pipelines>=3.0.0`

- Fix assert_almost_equal function on handling negative results

- get schema copying working on PostgreSQL 12
- get function create_enum working on PostgreSQL 12

- add `etl_tools.schema_check.AbortOnSchemaMisuse(schema_name)` Command
and the helper
`etl_tools.schema_check.add_schema_misuse_check_as_first_command_in_initial_task(pipeline)`
which adds it as first command in the intial task in every (sub-) pipeline
which has a `'Schema'` label.

- Rename package from `etl-tools` to `mara-etl-tools` to avoid a PyPi name conflict.
- Avoid deadlocks in data set attribute table creation

**required-changes**

- Adapt your requirements.txt like this: `-e git+https://github.com/mara/mara-etl-tools.git3.0.0egg=etl-tools
`

- Change MARA_XXX variables to functions to delay importing of imports

**required changes**

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