replace is_staff with has_permission

[pprolancer]

Hello, @douglasmiranda

https://github.com/douglasmiranda/django-admin-bootstrap/blob/1c837e39e2beaf309398e648c174125189394130/bootstrap_admin/templates/admin/base.html#L125

in above line we shouldn't check accessibility with "is_staff". this cause problems for customized permission admin sites.

we should replace that line with: {% if has_permission %}