* Add JS for qrcodejs
Ref: https://davidshimjs.github.io/qrcodejs/
* Simple function for rendering a QR code
* Refactor QR code view for Part
* Replace QR code view for SupplierPart
* Refactor QR codes for stock item and stock location models
* Remove base QRCodeView entirely
* Lazy load the pricing bom table when the "pricing" tab is selected
* Update django-debug-toolbar configuration
* Major refactoring for the 'can_build' function
- Use a single annotated query to the db, rather than a for loop (which is what a caveman would use)
- Query performance is greatly improved
- Also refactors existing variant-part-stock subquery code, to make it re-usable
* Use minified JS and CSS where possible
* Render a 'preview' version of each part image
- Saves load time when the image is quite large
- Adds a data migration to render out the new variation
* Adds 'preview' version of company images
* Defer loading of javascript files
Note: some cannot be deferred - jquery in particular
* Crucial bugfix for user roles context
- Previously was *not* being calculated correctly
- A non-superuser role would most likely display pages incorrectly
* Prevent loading of "about" on every page
- Load dynamically when requested
- Takes ~400ms!
- Cuts out a lot of fat
* Match displayed image size to preview image size
* Utilize caching framework for accessing user "role" information
- Reduces number of DB queries required by rendering framework
* Remove redundant query elements
* Remove 'stock' field from PartBrief serializer
- A calculated field on a serializer is a *bad idea* when that calculation requires a DB hit
* Query improvements for StockItem serializer
- Remove calculated fields
- Fix annotations
* Bug fixes
* Remove JS load test
- Loading of JS files is now deferred, so the unit test does not work as it used to
* Fix broken template for "maintenance" page
* Remove thumbnail generation migrations
- Already performed manually as part of ''invoke migrate"
- Running as a migration causes unit test problems
- Not sensible to run this as a data-migration anyway
* tweak for build table
