composer.json: include dependent PHP extensions

composer.json

@@ -14,5 +14,11 @@
             "models/",
             "templates/"
         ]
+    },
+    "require": {
+        "ext-mysqli": "*",
+        "ext-imagick": "*",
+        "ext-gd": "*",
+        "ext-fileinfo": "*"
     }
 }