* add last mod time lookup to data locator
* store data locator in Driver
* save metadata header in labels csv
* lint
* fix tests
* change datetime format to second precision
* initial cut at backed mode
* make flask multithreading conditional on debug flag
* update X access to support backed mode
* lint
* improve help message for backed mode
* fix tests
* add MatrixProxy to normalize supported matrix types
* add FAQ entry for --backed
* remove use of matrix.T
* clean up
* add ability to disable diffexp from CLI; add hueristic to detect likely slow diffexp calculation, and warn user
* fix tests
* do not print diffexp speed warning if diffexp is disabled
* tweak wording of diffexp speed messages
* add FAQ entry on --disable-diffexp
* revise heuristic for warning about slow diffexp
* use quick tooltip delay on diffexp button
* initial commit of URL support for launch
* lint
* modify tests to use new data locator
* add locator unit tests
* fix typo in faq
* more lint
* update faq per PR review
* move app creation to function
* create engine without load
* flake 8 fixes
* cleanup original scanpy test
* add default config
* handle missing data
* test data changes
* unify update
* load data isn't static anymore
* make app a class