Ebookconverter

- when the html file is large (>16M), in most cases we don't really want to make an EPUB or a MOBI. Making the MOBI can take hours with our current infrastructure. Changed the source file size filters so these formats are not made.
- when the source EPUBs are >32M, only old-format MOBIs are not made.
- add jekyll script
- stop trying to store qr codes in databaseta from backup workflow files
- add script to load metadata

- production directory moves from ~/converter to ~/ebookconverter to accomplish the python version migration.

- `--notify` and `--validate` are now flags that turn on validation and notification
- use simpler CLI to call Ebookmaker
- update requirements

- exceptions in notifier would cause stuck pid Files

- now using ebookmaker 0.12 (beta),
- use new notifier API
- refactored/added --notify and --validate command-line options
- add epub3 and kf8 filetypes

- added a script to reload a workflow file. Usage: reload_workflow [list of ebook numbers]
- add requirement for lxml<4.7