use Date.now() instead of new Date().getTime()

This is documented to be more performant.

The substitution was made on frontend code, too (i.e., the one in /static),
because Date.now() is supported since IE 9, and we are life supporting only
IE 11.

Commands:
  find . -name *.js | xargs sed --in-place "s/new Date().getTime()/Date.now()/g"
  find . -name *.js | xargs sed --in-place "s/(new Date()).getTime()/Date.now()/g"

Not done on jQuery.

src/node/db/API.js

@@ -522,7 +522,7 @@ exports.appendChatMessage = function(padID, text, authorID, time, callback)
   if(time === undefined || !is_int(time))
   {
     // set time to current timestamp
-    time = new Date().getTime();
+    time = Date.now();
   }
 
   var padMessage = require("ep_etherpad-lite/node/handler/PadMessageHandler.js");

src/node/db/AuthorManager.js

@@ -110,7 +110,7 @@ function mapAuthorWithDBKey (mapperkey, mapper, callback)
 
     //there is a author with this mapper
     //update the timestamp of this author
-    db.setSub("globalAuthor:" + author, ["timestamp"], new Date().getTime());
+    db.setSub("globalAuthor:" + author, ["timestamp"], Date.now());
 
     //return the author
     callback(null, {authorID: author});
@@ -127,7 +127,7 @@ exports.createAuthor = function(name, callback)
   var author = "a." + randomString(16);
 
   //create the globalAuthors db entry
-  var authorObj = {"colorId" : Math.floor(Math.random()*(exports.getColorPalette().length)), "name": name, "timestamp": new Date().getTime()};
+  var authorObj = {"colorId" : Math.floor(Math.random()*(exports.getColorPalette().length)), "name": name, "timestamp": Date.now()};
 
   //set the global author db entry
   db.set("globalAuthor:" + author, authorObj);

src/node/db/Pad.js

@@ -86,7 +86,7 @@ Pad.prototype.appendRevision = function appendRevision(aChangeset, author) {
   newRevData.changeset = aChangeset;
   newRevData.meta = {};
   newRevData.meta.author = author;
-  newRevData.meta.timestamp = new Date().getTime();
+  newRevData.meta.timestamp = Date.now();
 
   //ex. getNumForAuthor
   if(author != '')
@@ -739,7 +739,7 @@ Pad.prototype.addSavedRevision = function addSavedRevision(revNum, savedById, la
   savedRevision.revNum = revNum;
   savedRevision.savedById = savedById;
   savedRevision.label = label || "Revision " + revNum;
-  savedRevision.timestamp = new Date().getTime();
+  savedRevision.timestamp = Date.now();
   savedRevision.id = randomString(10);
 
   //save this new saved revision

src/node/db/SecurityManager.js

@@ -152,7 +152,7 @@ exports.checkAccess = function (padID, sessionCookie, token, password, callback)
               
               if(ERR(err, callback)) return;
               
-              var now = Math.floor(new Date().getTime()/1000);
+              var now = Math.floor(Date.now()/1000);
               
               //is it for this group?
               if(sessionInfo.groupID != groupID)

src/node/db/SessionManager.js

@@ -114,7 +114,7 @@ exports.createSession = function(groupID, authorID, validUntil, callback)
       }
     
       //check if validUntil is in the future
-      if(Math.floor(new Date().getTime()/1000) > validUntil)
+      if(Math.floor(Date.now()/1000) > validUntil)
       {
         callback(new customError("validUntil is in the past","apierror"));
         return;