Refactor UI and remove unused tests

- Deleted the generated UI file `untitled_ui.py` as it is no longer needed.
- Updated `search_statistic_page.ui` to enhance table properties, including grid style and sort indicators.
- Modified `search_statistic_page_ui.py` to reflect changes in the UI file and improve table header settings.
- Improved cleanup logic in `richtext.py` to ensure files are only deleted if they exist.
- Adjusted spacing in document generation for better formatting.
- Removed obsolete test files: `database_test.py`, `many_webrequest_test.py`, `test_database.py`, and `webrequest_test.py` to clean up the test suite.

icons/db_search.svg

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