Multi-select

Features:

• Multi-select for front-end file picker.
• Batch entering ability for ASINs of selected files.
• Post-processing display of batch.
• Add logging system (should play nicely with Docker ENV variables to set it).

Fixes:

• Refactor Author model to handle authors without ASINs. Fixes #8
• HTML spacing fixes
• Fix breadcrumb links causing an error on new session: #14

Sreens

Take multiple inputs in a list

Ask for ASINs all together

Show all results (this needs to be refined)