Extendability improved

Dexie.Syncable add-on on its way. Will enable sync remote nodes and
provide new C(R)UD events to listen on when something changes, no matter
if change originates from local or remote db.

"ready" event with support for returning a Promise to block db until
promis fullfilled.

Hook events with support for this.onsuccess and this.onerror.
Needed for implementing FullTextSearch views (See FullTextSearch2.js)