Update syncer and adaptors to allow saving tiddlers in bulk

[inmysocks]

This is started in BrowserWSAdaptor.js with a new function saveTiddlers, it is like saveTiddler, but it takes an array of tiddler objects.
The idea is that when a adaptor supports it the syncer can create a task that saves multiple tiddlers at once in order to speed up the process.

Tasks:

• create a supportsMultiSave property on the sync adaptor so the syncer can test for compatibility
• Create saveTiddlers in BrowserWSAdaptor
• Add a handler for the saveTiddlers message in NodeBasicHandlers.js
• update syncer.js to have saveTiddlers tasks