Panel: Generate header id manually

We use [email protected] to generate our header id.

[email protected] is reported to be unsafe and contains vulnerabilities [1].

As a step towards removing [email protected] as a dependencies, let's replace
all usage of the 'string' methods with suitable equivalents.

[1] - jprichardson/string.js#212

Author: yamgent

src/Panel.vue

@@ -299,7 +299,7 @@
       if (this.headerContent) {
         const panelHeaderText = jQuery(this.headerContent).wrap('<div></div>').parent().find(':header').text();
         if (panelHeaderText) {
-          this.$refs.cardContainer.setAttribute('id', string(panelHeaderText).slugify().toString());
+          this.$refs.cardContainer.setAttribute('id', String(panelHeaderText).trim().toLowerCase().replace(/\s+/g, '-'));
         }
       } else if (this.$refs.headerWrapper.innerHTML) {
         const header = jQuery(this.$refs.headerWrapper.innerHTML).wrap('<div></div>').parent().find(':header');