Feature cn 158 add button on open book dialog

[mandolyte]

Describe what your pull request addresses

• [ ] handles enabling and disabling of the "add" button on the add book popup dialog

Test Instructions

• [ ] there are three cases, one each for each source.
• [ ] for dcs, the add button should only be enabled when all three pieces are set: org, repo, and book
• [ ] for url, the add button should only be enabled when a non-empty value is entered into the text box
• [ ] for upload, the add button should only be enabled when a file is selected to be uploaded
• [ ] Additionally, when a book is selected for upload, the upload button text should include the filename of the book uploaded

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