caltechlibrary/handprint: Release 1.5.1

There are no functional changes in this release; all of the code changes are internal, to speed up Handprint startup times and further clean up some code dependencies.

All changes in this release:

• To speed up initial application startup time, import statements have been moved from (usually) the tops of files, to where the packages are actually used in the code. Profiling using the Python -X importtime option helped identify expensive packages to make this efficiency gain possible.
• The user interface code in ui.py has been replaced with importing Bun.
• The version of commonpy needed is now 1.3.9.
• The dependency on dateparser has been removed because Handprint doesn't depend on that package. (It's a transitive dependency coming from something else, but by itself, it doesn't belong in Handprint's requirements.)