Is there a rich text editor for Craft CMS which supports both HTML source code edit as well as adding images by URL (not uploading to assets)?
You can do it with Redactor.
You can configure your toolbar to have a view HTML button.
Also, a caveat, Redactor has an html-purifier function, which will eat some bits of code in the name of making it "clean." But that's relatively easy to configure as well. Just make sure to look at the plugin documentation.