Fix: Cannot react to task descriptions

Problem: You cannot react to Tasks, only Task comments. 😔

Technical discussion

Task descriptions are currently stored as a text field in the tasks table. At the moment, only comments support reactions, so we will have to add a new task_reactions table, and add support for this into the existing reaction frontend code.

This is a bit of a pain, as we already have separate reactions for task comments, project update comments, and thread comments. Gah.

Steps

1. Backend: Migration to add new table
2. Backend: Context/schema/controller code for new reactions
3. Backend: Request reactions along with task
4. Frontend: Display task reactions
5. Frontend: Refactor comment templates to simplify
6. Release!