Fix wrong behavior of paragraph alignment buttons

This patch changes `DirectFormattingController` to read the styling not just over text nodes but over any character/text element. This then allows us to give non-empty styling info to the style summary generator, which lets us correctly display the state of the toolbar buttons, thus getting rid of #629.

The patch also stops disabling of alignment buttons when an image is selected, as per [this comment](https://github.com/kogmbh/WebODF/pull/626/files#r13418358) by @peitschie. This also has the side-effect of sweeping #630 under the rug.