Add transaction description autofill functionality

[odinsride]

Add transaction description autofill functionality.

Notes from 1/10/21:
Attempted autocomplete with stimulus and autocomplete.js, but the problem is that it requires a controller action that constantly queries the DB with every keystroke. Prefer to have the unique descriptions fetched one time and filtered client side. Will revisit implementing this as a Vue component or trying a different approach in Stimulus later.