Circular dependencies in jbrowse/core

[cmdcolin]

these cause bundler warnings and not good practice

rollup produces two errors from jbrowse/core

!) Circular dependencies
../node_modules/@jbrowse/core/ui/Dialog.js -> ../node_modules/@jbrowse/core/ui/ErrorMessage.js -> ../node_modules/@jbrowse/core/ui/ErrorMessageStackTraceDialog.js -> ../node_modules/@jbrowse/core/ui/Dialog.js

../node_modules/@jbrowse/core/BaseFeatureWidget/BaseFeatureDetail/Attributes.js -> ../node_modules/@jbrowse/core/BaseFeatureWidget/BaseFeatureDetail/ArrayValue.js -> ../node_modules/@jbrowse/core/BaseFeatureWidget/BaseFeatureDetail/Attributes.js

resolving circular dependencies sometimes involves putting a bunch of stuff in one file instead of different files, but there are also other techniques