Snowddl

- Fix missing grants for `schema_owner`, `schema_write`, `schema_read` business role options without wildcards.

- Speed up SnowDDL execution by loading grants and future grants of existing roles in parallel.

- Added a basic wildcard option while setting `schema_owner`, `schema_write`, `schema_read` options for business roles to match "all schemas in database". For example: `snowddl_db.*`. At least one schema matching wildcard condition should exist in config.

It is useful for managing generic script roles when new schemas are added and / or removed frequently.

- Identifier objects were completely reworked. Now every identifier type has its own class with every part being named.
- Simplified blueprint objects. Removed `database`, `schema`, `name` fields from schema object blueprints. All this information is available as parts of `full_name`.
- Moved complex logic for "building" identifiers into dedicated module `ident_builder`.
- Performed initial preparation and testing for "singledb" entry point, which will be added in the next version.

- Rework internal architecture of entry-points for SnowDDL CLI interface. Now it will be much easier to add new entry-points and to partially re-use existing entry-points in your own code.

- Added parameters `login_name`, `display_name` for `USER` object type.
- Added argument `--placeholder-values` for CLI interface. It allows passing custom placeholder values in JSON format without creation of temporary file for `--placeholder-path`.