CSS optimization support remove unused CSS selector

[yuanyan]

Search the whole plain HTML and template files in project, find and remove the unused CSS selector content in CSS files.

Orign:

.btn{}
.primary-btn{}
.js-primary-btn-active{}   /* JavaScript dynamic add */
.danger-btn{}                 /* Unused in current project */
.warn-btn()                    /* Unused in current project */

<button class="btn primary-btn">

After optimization:

.btn{}
.primary-btn{}
.js-primary-btn-active{}