underscore.js is needed

[zreptil]

took me a while to figure it out. there are some references to functions that start with "_." like _.isNumber(...) in the file jv-datepicker.html. it looks like there must be an import of underscore.js somewhere, but this file is not bundled with the deployment. after finding it in the web and adding it, the component works as expected.

[motss]

@zreptil1 Duplicated issue. Please refer to #2. Thank you.