Python task manager from scratch, part 29: Cosmetic improvements

After the big back-end switch, I'm still cleaning up. Today:

1. Making the "mark complete" buttons go on the same line as the task descriptions;
2. Making the task descriptions labels of those HTML buttons instead of text that happens to be near them;
3. Giving those buttons unique IDs;
4. Fixing a data-loss bug where I'd add tasks and then lose them.

Some things to know about the material:

1. The bug was caused (I think!) by the fact that I hadn't committed them. It's useful to know a bit about what "committing" is: I found this post useful. The idea of a "unit of work" is also valuable, and I went far too long without studying it. (My favorite introduction to it is in Architecture Patterns with Python.)
2. Right now we have one HTML form per task. Another, perhaps better, choice is to have a single form. Do not take this as any kind of principled position on the matter. But do take it as a reminder that there are a lot of perfectly good approaches to implementing things in HTML and CSS that sound a bit strange when you first hear them ("to render this task list we'll create a page with 32 forms on it").

Here's the current commit in the veery/ repository.