Better Tag Autocompletion and Nicer Date Handling

A few minor improvements were added to tedium today.

The tag auto-completion now caches the list of tags in your browser, so it should be quicker to pop up a list of matching tags when you start typing them in.

And the other change is to the due dates for tasks. They are now displayed in a more human-friendly format, and when choosing the due date the calendar drop-down now highlights both today and the currently chosen due date on the display.

Not huge changes, but ones that will make tedium more polished.