Improving the default categories

We've recently gotten PRs (#167, #173) making improvements to the default categories. This is good, but writing good categorization rules can be tricky.

Here are a few common pitfalls:

- Apps that have non-unique names (i.e. Kate, Navigator, Files)
- Solution: Make sure that the whole string has to match
- Solution: Only match certain event keys (not possible yet)
- Titles mentioning apps can get classified as apps.
- Loosely written expressions that over-match. It's a lot easier to find Uncategorized events than to find Miscategorized events.

I'm sure there are more, these are only the ones off the top of my head.

In this issue I will gladly accept suggestions for common apps and websites that should be added to the defaults, as well as suggested patterns for matching them in a way that minimizes the risk of misclassification.