[Web Clipper] [Evernote Importer] Add option for save images using base64

[andresmlna]

Hi.

Problem
Actually, the web clipper don't save the images for new notes, only adds the remote url as like html tag. It's is a problem, because when the Standard Notes app goes internet offline, the app can't load the image for the external url.

The Evernote importer can saves the images as file attachment. But with several notes, adds several files attachments on the app, it's difficult manages too many images files.

Solution
Add the option for save the notes images as base64 into the notes code. It's a clean method for unity the images and notes as a single element.

Greetings.