With this PR, when JS is activated and WASM supported, the article editor will be dynamically replaced with `contenteditable`s elements. This makes the editing interface simpler and less like a regular form. It will also allow us to easily add visual formatting with native browser APIs (and to insert images or videos directly). Here is a little demo:
There is still a lot to do, but it is a good first step.
Fixes#255
* Allow customizing max form size from env vars
* Add error page for unprocessable entities
And change default http port to 7878
* Improve char counter: under the editor, more discrete, and give it a default value
Rust can compile to WASM, so let's use it for front-end code as well.
To compile the front-end:
```
cargo install cargo-web
cargo web deploy -p plume-front
```
