Fix undo/scheduling not being cleared on DB writes

[dae]

The undo code was added after David's initial work, so it was missing
from his code. Fixed by refactoring so they both use the same code
path.

Individual change is 55e49a8 - I've squashed it into the earlier commit. I also dropped the second commit on the branch which built web assets, since it looks like @krmanik's approach is the way forward.

Recommend you either

a) pull into a new branch like ankidroid-2.1.54.1, avoiding rebase, or
b) tag current ankidroid-2.1.54 with ankidroid-2.1.54.0 (so we have a record of where it was before), then force-push this branch into the existing one

[dae]

I've squashed the following commit: ankitects@fe51d9b

[mikehardy]

I liked option (a) and went with it

similar to last time:

On the command line, assuming you have "origin" set up as a remote (to a personal fork), "upstream" set up as a remote pointing at ankitects/anki, and you have "ankidroid" set up as a remote, it looked like this:

git co main
git fetch upstream
git rebase upstream/main
git push origin
git push ankidroid
git co -b ankidroid-2.1.54 # this works because it is unambiguous to this point, it only existed in ankitects remote to start
git reset --hard 67e4edc # that was the most recent commit hash on ankitects/main for this PR
git push ankidroid # this gets us a clean ankidroid-2.1.54 branch at the divergence point, in our repo now
# Now on this PR edit it and change it to target our new branch, poof 2 commits as indicated
git merge --ff-only upstream/ankidroid-2.1.54  # now we have identical commit hashes from the PR, merged
git push ankidroid

Now we've pushed the commits here without modifying their commit hashes, so the commit hash in Anki-Android-Backend is stable