Save pending sharejs operations

[fasib]

The pending shajrejs operations should be safed to the localStorage, just in case that someone closes the window/tab with pending sharejs doc updates.

e.g:

if not connected && pendingData
  localStorage.setItem("DConv:partB", JSON.stringify(doc.pendingData));

if reconnect
  stillPending = JSON.parse(localStorage.getItem("DConv:partB");
  localStorage.removeItem("DConv:partB");
  doc.pendingData.push_each(stillPending);