Update Anki function names

[rwmpelstilzchen]

Problem

AnkiConnect calls Anki functions by their old names, which results in warning messages. For example, calling findCards makes Anki output the following warning:

addons21/2055492159/__init__.py:1129:'findCards' is deprecated: please use 'find_cards'

Solution

Update the names to the contemporary ones. AnkiConnect’s API may remain as it is, but the calls for Anki’s internal functions should be updated.