Allow dots in app names (closes #260)

App names may now contain dots, such as sneak.berlin: runs of
lowercase letters and numbers joined by single dots or by hyphens,
2 to 63 characters. Docker accepts every such name in the app's image
name, upaas-<name>; a dot needs a letter or number on both sides
because Docker requires it. The rule also keeps a dot off either end,
so the name is safe as a directory and log file name.

The new and edit app forms use the same pattern. Their old one was not
a valid regular expression under the flag browsers compile it with, so
browsers ignored it.

A test deploys an app named sneak.berlin against the fake Docker API
and checks the image and container names with Docker's own rules.

Model: opus-5-5

templates/app_edit.html

@@ -30,10 +30,12 @@
                     name="name"
                     value="{{.App.Name}}"
                     required
-                    pattern="[a-z0-9-]+"
+                    minlength="2"
+                    maxlength="63"
+                    pattern="[a-z0-9]+((\.|-+)[a-z0-9]+)*"
                     class="input"
                 >
-                <p class="text-sm text-gray-500 mt-1">Lowercase letters, numbers, and hyphens only</p>
+                <p class="text-sm text-gray-500 mt-1">Lowercase letters, numbers, hyphens, and dots, such as my-app or example.com</p>
             </div>
 
             <div class="form-group">