Engineer image: upload the Engineering Layer from the web app

New Engineering Layer tab on the engineer image page. A site uploads
Engineering_Install_v<ver>.exe (keeps prereqs) or a .zip of the whole
extra_engineering payload. The upload is streamed to disk, checked (MZ
header, no unsafe zip paths) and swapped in; the replaced payload is
archived (two kept) with a Restore button. Install-EngineeringLayer.ps1
stays repo-owned and now installs the newest Engineering_Install_v*.exe.

KB: Part 4 becomes Site Content (enrollment package, Engineering Layer,
Blancco site settings, Shop Floor apps) plus a new Adding Shop Floor
Apps section for preinstall.json/postppkg.json. WJ examples removed.

webapp/templates/_image_header.html

@@ -97,7 +97,7 @@
   </div>
 
   <nav aria-label="Image sections"><ul class="image-tabs">
-    {% for t in image_tabs %}
+    {% for t in image_tabs if not t.images or image_type in t.images %}
     <li><a href="{{ image_tab_url(image_type, t.id) }}"{% if t.id == _tab %} aria-current="page"{% endif %}>
         {{ t.label }}
         {% if t.id == 'drivers' %}<span class="tab-count" title="Entries in HardwareDriver.json">{{ _hdr.driver_count }}</span>