fix(a11y): keep focus on input after selecting an dropdown item

Fixes second example of #1926.
To be accessible, it should be possible to keep using the input easily
after selecting and item on multi-select input.
Previously, when using mousedown to pick an item from the dropdown, the
input would lose focus and ignoring blur wasn't enough in order to keep
the input focused.

Author: YoYuUm

src/selectize.js

@@ -692,6 +692,9 @@ $.extend(Selectize.prototype, {
 		var self = this;
 
 		if (self.ignoreBlur) {
+			if (self.isFocused) {
+				self.focus();
+			}
 			return;
 		}