Mara-superset

- fix .scripts folder missing in pypi package

- improving metadata sync
- add option to install Apache Superset locally via .scripts/superset.mk (for dev/test purpose)

- fix metric expression avoid divisions by 0 (taken from mara_schema implementation)
- fix composed metrics with NULL values (taken from mara_schema implementation)
- fix wrong format for NumberFormat.PERCENT in metadata sync.

- first version

- fix makefile copy scripts target .copy-mara-superset

----------