Rewrite comments in Rails

Currently, comments are written in React, using TypeScript + the GraphQL API. this seemed like a good idea in the beginning, but currently adds a lot of complexity to the system: 1. Comments is the only piece of Decidim that actively uses the API. This forces the new developers to learn yet another piece of software, steeping the learning curve. 2. Comments use TypeScript instead of bare JS. This adds type safety, but steepens the learning curve. 3. In development, the API breaks. This is not a Decidim problem per se, it's a bug on the library we use to develop the API, but again it makes it harder to develop. All this makes it harder to modify/improve the comments section, but we'd reduce a lot of lines of code, we'd slim dependencies down and we'd remove some complexity. Also, we'd gain some consistency in development. The downside is that this could be a big refactor, but I think it's a nice investment.