simplepicker: Don't modify elements outside the simplepicker elements.

The bug here was initElMethod was called with wrong element, we fix this
by calling it in the init method where we first query the simplepicker
and then calling the method so scope the this.$ and this.$$ to it.

Fixes: #25.

lib/index.ts

@@ -65,9 +65,8 @@ class SimplePicker {
     }
 
     this.selectedDate = new Date();
-    this.initElMethod(el);
     this.injectTemplate(el);
-    this.init(opts);
+    this.init(el, opts);
     this.initListeners();
 
     this._eventHandlers = {};
@@ -86,11 +85,12 @@ class SimplePicker {
     this.$$ = (sel) => el.querySelectorAll(sel);
   }
 
-  init(opts: SimplePickerOpts) {
-    const { $, $$ } = this;
+  init(el: HTMLElement, opts: SimplePickerOpts) {
+    this.$simplepickerWrapper = <HTMLElement> el.querySelector('.simplepicker-wrapper');
+    this.initElMethod(this.$simplepickerWrapper);
 
+    const { $, $$ } = this;
     this.$simplepicker = $('.simpilepicker-date-picker');
-    this.$simplepickerWrapper = $('.simplepicker-wrapper');
     this.$trs = $$('.simplepicker-calender tbody tr');
     this.$tds = $$('.simplepicker-calender tbody td');
     this.$headerMonthAndYear = $('.simplepicker-month-and-year');