Add a reset method to the PDFHistory implementation

This patch addresses a couple of smaller issues with the `PDFHistory` class:
 - Most, if not all, other viewer components can be reset in one way or another, and there's no good reason for the `PDFHistory` implementation to be different here.

 - Currently it's (technically) possible to keep adding entries to the browser history, via the `PDFHistory` instance, even after the document has been closed. That obviously makes no sense, and is caused by the lack of a `reset` method.

 - The internal `this._isPagesLoaded` property was never actually reset, which would lead to it being temporarily wrong when a new document was opened in the default viewer.

web/interfaces.js

@@ -101,6 +101,8 @@ class IPDFHistory {
    */
   initialize({ fingerprint, resetHistory = false, updateUrl = false, }) {}
 
+  reset() {}
+
   /**
    * @param {Object} params
    */