A new feature in v0.5.12. A dialog that allows you edit the list of categories for a site, adding or deleting categories, or changing the text of the name or description of a category.

How to

1. Create a new post.
2. Assign it to the site whose categories you want to edit. To do so, click on Choose site in the lower left corner of the editing window.
3. Choose Edit all categories from the context menu, linked into the three dots in the upper right corner of the editing window.
4. You should see a dialog that looks something like this.

Three things

There are three basic things you can do.

1. Add a new category, by clicking the + button in the lower left corner of the dialog.
2. Edit the text of an existing category. 
3. Delete a category, by clicking the trashcan next to it

Nothing happens until you press the Save button. It then confirms what it's going to do. There is no undo, so if you have any concerns, you should decline to save it.