feat: add ability to disable overlay (#101)

This commit adds disable freeze overlay functionality, usage `disableOverlay` option (defaults to false) can be passed to the preboot initial config as follows:
```
PrebootModule.withConfig({ appRoot: 'app-root', disableOverlay: true })
```

Author: ankitu

README.md

@@ -99,6 +99,7 @@ replayer.replayAll();
 * `buffer` (default `true`) - If true, preboot will attempt to buffer client rendering to an extra hidden div. In most
 cases you will want to leave the default (i.e. true) but may turn off if you are debugging an issue.
 * `minify` (deprecated) - minification has been removed in v6. Minification should be handled by the end-user
+* `disableOverlay` (default `true`) - If true, freeze overlay would not get injected in the DOM.
 * `eventSelectors` (defaults below) - This is an array of objects which specify what events preboot should be listening for 
 on the server view and how preboot should replay those events to the client view. 
 See Event Selector section below for more details but note that in most cases, you can just rely on the defaults

src/lib/api/event.recorder.ts

@@ -142,8 +142,10 @@ export function getAppRoot(
   // else the client root is the same as the server
   root.clientNode = opts.buffer ? createBuffer(root) : root.serverNode;
 
-  // create an overlay that can be used later if a freeze event occurs
-  root.overlay = createOverlay(_document);
+  // create an overlay if not disabled ,that can be used later if a freeze event occurs
+  if (!opts.disableOverlay) {
+    root.overlay = createOverlay(_document);
+  }
 
   return root;
 }
@@ -205,6 +207,7 @@ export function createListenHandler(
   // IE uses a prefixed `matches` version
   const matches = _document.documentElement.matches ||
     _document.documentElement.msMatchesSelector;
+  const opts = prebootData.opts;
 
   return function(event: DomEvent) {
     const node: Element = event.target;
@@ -262,8 +265,8 @@ export function createListenHandler(
       prebootData.activeNode = undefined;
     }
 
-    // if we are freezing the UI
-    if (eventSelector.freeze) {
+    // if overlay is not disabled and we are freezing the UI
+    if (opts && !opts.disableOverlay && eventSelector.freeze) {
       const overlay = root.overlay as HTMLElement;
 
       // show the overlay

src/lib/api/inline.preboot.code.ts

@@ -36,6 +36,7 @@ export const initFunctionName = 'prebootInitFn';
 export const defaultOptions = <PrebootOptions>{
   buffer: true,
   replay: true,
+  disableOverlay: false,
 
   // these are the default events are are listening for an transferring from
   // server view to client view

src/lib/common/preboot.interfaces.ts

@@ -29,6 +29,7 @@ export interface PrebootOptions {
   eventSelectors?: EventSelector[]; // when any of these events occur, they are recorded
   appRoot: string | string[]; // define selectors for one or more server roots
   replay?: boolean;
+  disableOverlay?: boolean;
 }
 
 // our wrapper around DOM events in preboot