Mara-pipelines

- add entry point `mara.commands` (for [mara-cli](https://github.com/mara/mara-cli) support)
- add mara-pipelines click command group (104)
- add dynamic Task (106)
- add max_retries for parallel tasks (105)
- fix html_doc_items tuple of command ReadScriptOutput

- upgrade to bootstrap 4.6 (from alpha 4) (66)<br>
*Caution:* Some CSS classes changed between Boostram Alpha 4 and 4.6. You might need to upgrade other mara packages as well, e.g. mara-pipelines and mara-app.
- add HttpRequest command 78 (79)
- add WriteFile command (89)
- add support for formats in file operations (95)
- add typing (91)
- add before/after task to ParallelTask only when not command list is not empty (93)
- fix get_user_display_name on docker (90)
- fix small issues (91)
- fix SQLAlchemy warning about declarative_base moved in 2.0 (99)

**required changes**
You might need to investigate your custom CSS styling, see boostram upgrade above.

- Add option to hide system stats in the UI 72
- Add option to disable the collection of system statistics (72)
- Add syntax highlighting for TSQL and SQLite3 (86)
- Support pipeline execution without 'mara' database (71)
- Fix getting exitcode from process issue since python 3.8 (87)
- Use client-side rendering for graphviz when shell command is not available (70)

- Fix CopyIncrementally with no data (54)
- Add ability to specify modification value type in CopyIncrementally (53) 66e7dc1 Jan Katins <jan.katinszenjob.com> 4. Mar 2021 at 22:06
- Fix read stderr during command execution (47)
- Use echo_queries from mara_db.config.default_echo_queries (58)
- Include all versioned package files in wheel

- Fix for visible passwords in the logs despite `mara_pipelines.config.password_masks()`
set. Bug was introduced in 3.0.0.

- Modify shell command to support the Google BigQuery integration
- Add file_dependencies argument to Python commands