[Qt] tweak new peers tab in console window

This intened as a preview, because it's work in progress.
@laanwj There are still problems with the display of the table in terms of resizing, also it looks rather ugly, if i get an IPv6 address in the form [2002:2518:aa7f:0:21be:d522:222e:38c7]:18333 as that is realllllllly long. I'm also not happy with what happens when peers dissappear (and perhaps if it was the last node also).

- remove columnResizingFixer
- add local address (if available) in detailed node view
- remove some .c_str() by using QString::fromStdString()
- rename Address to Address/Hostname
- rename secs to just s for ping time
- use MODEL_UPDATE_DELAY from guiconstants.h for the peer refresh time
- make PeerTableModel::columnCount() return no hard-coded value
- remove and cleanup dup private: section in RPCConsole header