new field 'separator'

This field create a new heading with description text, not save in
database. It is just design display field with below listed options:
1. id = 'unique' (as per redux framework required)
2. type = 'separator'
3. title = 'string'
4. head-tag = 'string' (h1, h2, h3, h4, h5, h6 or any html tag name)
5. icon = 'string' (name of font icon class ie. 'el-icon-gift')
6. icon-size = 'recommended string' (like '14px', '1em')
7. desc = 'string'