Add OT for OpSetParagraphStyle

This patch:

1. Renames `DirectFormattingController` to `FormattingController`, since it is more convenient to have the new method `applyParagraphStyle` in it, instead of peppering the codebase with direct instantiations of `OpSetParagraphStyle`.
2. Extends `OpSetParagraphStyle` with an additional `length` parameter which is necessary to write transformation logic against several other operations like `RemoveText` and `SplitParagraph`.
3. Adds OT logic against `InsertText`, `RemoveText`, `SetParagraphStyle`, and `SplitParagraph`, with tests for all possible combinations.
4. Since this operation is now OT-complete, enables the alignment and indentation button sets in the editor's toolbar.

Tested in collab mode. :sunglasses: