Adds a panel on the right that displays all the tags you have, along with their tag count.

When clicking on a tag, a search for the tag is activated. To ==toggle a tag== in search, Ctrl-click it instead.

### Sorting

The tags are sorted from most frequently used to least frequently used. You can change the sort order to alphabetical or reverse it.

### Nested tags

If you write your tags like `#inbox/to-read` and `#inbox/processing`, you can enable "show nested tags" to view them as a tree instead of a flat list.

Under the default flat view, the tag pane will look like:

```
- inbox/to-read
- inbox/processing
```

Under the nested tag view, the tag pane will look like:

```
- inbox
	- to-read
	- processing
```

