Add feature 80717: Add the ability to use AIM contacts with ICQ and vice versa.

- Add AIMContactBase class, that contains functions common for AIM contacts in AIM and ICQ accounts.
- Add ICQContactBase class, that contains functions common for ICQ contacts in AIM and ICQ accounts.
- Add ICQContact to AIM plugin and AIMContact to ICQ plugin.
- Move sanitizedMessage function to AIMContactBase and ICQContactBase classes, because we want parsing based on other side protocol.
- Add OscarProtocol which is now base class for ICQProtocol and AIMProtocol.
- Implement older away message format for ICQ, so AIM can see away message for ICQ contact.
- Cleanup duplicate code.