Refactor and add securities controller

lib/tradex_web/controllers/security_html/show.html.heex

@@ -0,0 +1,20 @@
+<.header>
+  Security {@security.id}
+  <:subtitle>This is a security record from your database.</:subtitle>
+  <:actions>
+    <.link href={~p"/securities/#{@security}/edit"}>
+      <.button>Edit security</.button>
+    </.link>
+  </:actions>
+</.header>
+
+<.list>
+  <:item title="Name">{@security.name}</:item>
+  <:item title="Ticker">{@security.ticker}</:item>
+  <:item title="Wkn">{@security.wkn}</:item>
+  <:item title="Isin">{@security.isin}</:item>
+  <:item title="Expiration date">{@security.expiration_date}</:item>
+  <:item title="Strike price">{@security.strike_price}</:item>
+</.list>
+
+<.back navigate={~p"/securities"}>Back to securities</.back>