refactor(templates): Bootstrap utilities instead of the upstream rules that redid them

webvirtcloud.css still carried the upstream panel's rules for what
Bootstrap 5.3 has as utilities and components:
- the page's bottom space (body padding) is pb-5 on base.html's body,
  and the console page no longer has to undo it;
- the VM page's action tabs (.action-button, .action-block with a
  fixed 65px width) are text-center with a d-block icon; its tab panes
  (#power ... #undefine, one rule each) mt-3;
- the bordered sub-tab panes (.tab-pane-bordered, a fixed #eee border
  that dark themes could not change) border border-top-0 p-3;
- the search box and header buttons (.search, .btn-header) m-1 and
  mt-1; the SSH key select (.keyselect) a form-select;
- the boot order list (.multipleselect, fixed size, #c0c0c0 border) a
  list-group of form-check-input items; its unused .multipleselect-on
  goes;
- table cells centred by a global rule are align-middle on each table.
Two rules against Bootstrap's behaviour go: menus opened on hover on
wide screens (Bootstrap opens them on a click, and keyboard and touch
users had no hover), and "a { outline: 0 }", which hid the keyboard
focus ring.

The paragraph and page-header margins and the 900px container stay
for a separate change: they set every page's layout.

interfaces/templates/interface.html

@@ -55,7 +55,7 @@
             <h5>{% trans 'Slaves' %}</h5>
             {% if itype == 'bridge' %}
             <div class="table-responsive">
-                <table class="table table-bordered">
+                <table class="table table-bordered align-middle">
                     <thead>
                     <tr>
                         <th scope="col">{% trans 'MAC' %}</th>