created cleandb.py to clean database file

[destevae]

#67 #66
Created cleandb.py as requested to clean up the database by deleting all talks from previous years. After deleting all previous year talks, it checks for any room day entries without any talks in them, and deletes those.

Usage: python cleandb.py <path to db file> <SCALE number>

• Ex. If you're trying to delete all talks from the database not corresponding to 2025 SCALE (22x), run python cleandb.py scale22x.db 22
• If you accidentally enter a SCALE number with no entries in the database, the script does not delete any talk entries.

One small issue: Since cleandb.py doesn't directly delete room days with dates from previous years, after using the script, some current year talks may be left with previous year room days. This doesn't affect anything except for the new functionality in #70 since the date will be automatically included in the Youtube video details.