Author-friendly UI for coded solutions

### As a Joplin editor, I want it to be intuitive to add things like tables and apps to a page, so that I can easily publish relevant content for my audiences without needing an expert or admin to help me.

**Is your feature request related to a problem? Please describe.**
We've implemented short-term solutions that require using shortcodes, markdown, or HTML to add features within rich text blocks. These features include:
- buttons
- tables
- apps

We need to design author-friendly solutions for adding and managing these in Joplin.

**Describe the solution you'd like**
There might be different solutions for different features; this is just a mega-issue for the future :)

**Describe alternatives you've considered**

**Additional context**