Fix bug with making uploadMethod a function
Expose canToggle
Add a basic button formatter factory
Docstrings
Fix renderButton

Also, make _collapseFilter a static method
Add failing test for initializing grid with fileButton function
Save the button idx in the element
Button callbacks execute successfully

downloadItem uploadItem, and deleteItem stubbed
Update dropzone options on drop, then call onDrop callback
Basic click upload functionality

Buggy, though. Can't upload > 1 file at a time
Add callback options for button
Fix tests
default showButtons to false