Trick for emptyInsertThreshold

Give a pure-css workaround to emptyInsertThreshold option.

Update package.json: The entry file uses the compiled

Not tree-shake repaint function by compressors like terser

Closes #1658

Solves "insert Before error" issue on nested lists

moves issue templates to the correct folder

creates new github issue templates

That solves an issue with nested sortables.
example of error https://codepen.io/romualdogrillo/pen/jOPoRJe
An error appears when all following conditions are met:
1)You have two nested sortable containers
2)option “pull:clone” i set at least on the parent container
3)You drag an item from the parent container into the nested container

The item is moved but not cloned and you get the error: 
“Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted”

Fixed a typo in the description of the 'closest' method

Fix clicking select tag 

Minor fix for IE compatibility in st/app.js UI of thresholds demo