Added XEP-0138 Stream Compression support to XMPPFramework

    1. Separated XMPPStream internal Extension into the XMPPStreamInternal.h, which could be called from XMPPFeature;
    2. Moved asyncSocket write/read data into a wrapper method -[XMPPStream write/readData ...], in which a registeredStreamPreprocessor could do preprocess (eg, XMPPCompression could deflate / inflate data);
    3. Added XMPPFeature into calling procedure for XMPPStream;
    4. Added XMPPCompression feature, which applies to XEP-0138 Stream Compression
    5. Added XMPPCompression support into DesktopXMPP and iPhoneXMPP projects

Tested on OpenFire 3.8.2 and ejabbared 2.1.13