Add ability to inline edit translations

[frapell]

If the backend API allows it, you can provide an updateTranslation endpoint to the translateWidget init parameters. If that is the case, there's an advanced feature that gets enabled, that will show an edit pencil over translated chunks. When clicking on it, an edit <textarea> will show up where the translation can be edited and saved. This is how it works:

When the translation feature kicks in, you get the content translated (As normal):

While holding Ctrl and hovering over it, you will get the edit pencil with a border showing what is going to be edited:

After clicking the edit pencil, you get a <textarea> with the translation to edit:

Finally, clicking Save will send the updated translation to the backend endpoint, and update the element:

[frapell]

@au5ton Hey! here's another one for you to review :)

We implemented in our backend the ability to cache translations to avoid going back to the translation service on every request. In addition to that we implemented this feature that allows editing in place (We are using this on top of a CMS so we have permissions in place, and this would only be available to editors with proper permissions, by providing the endpoint or not).

Anyway, I implemented it as a branch in our fork on top of #31 so you should merge that first, and then this one (If you actually want this feature in)

[au5ton]

This is fantastic! I've also used this project in a cached scenario and this feature would be phenomenal!

[au5ton]

Would you be willing to update openapi.yaml and README.md with how to use this new feature? @frapell