Drop jquery dependency

[laszlokorte]

Maybe we do not need to use jquery at all.

Currently we use:

$.extend for merging the config object with the default config - could use pure js to do the merge
$.prototype.text() to access the input fields content - could use innerText and textContent
$.prototype.stop and $.prototype.slideToggle - could use css animation
$.prototype.next, $.prototype.is and $.prototype.closest - could use document.querySelector,
$.prototype.on and $.prototype.off for event binding - addEventListener should work in all browsers now
$.ajax for ajax request - could use raw ajax api