Add file plugin to display plain text files

www/file/app-file.less

@@ -52,6 +52,16 @@
             max-width: 100%;
             max-height: ~"calc(100vh - 96px)";
         }
+        .plain-text-reader {
+            align-self: flex-start;
+            width: 90vw;
+            height: 100%;
+            padding: 2em;
+            background-color: white;
+            overflow-y: auto;
+            word-wrap: break-word;
+            white-space: pre-wrap;
+        }
     }
 
     #cp-app-file-upload-form, #cp-app-file-download-form {