Script time execution optimization

1. Quickbase API PHP SDK sends all requests to Quickbase server using cUrl extension. In original code new cUrl instance creates for each data transmitting. By default QB use secured connection (https - ssl authentication). When cUrl try to connect to some server, part of this time goes to pretransfer action ("handshake" action - ssl authentication). This time sometimes quite big. If server is situated in Europe and tries to connect with Quickbase server this time could take up to 400-500ms. Fix allow to use the same connection in one Quickbase Class instance. This will save time for ssl handshake for each action. (For example 400ms * actions number. For 10 actions this time could take 4s)
2. Incorrect url was fixed in sign_out action