Remove -beta suffix

It conflicts with our normal naming of releases/builds. Fixes #4221.
[Qt] tweak new peers tab in console window

- remove starting height as table header and replace with ping time
- 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
- add new defaults for column sizes
- remove behaviour which keeps disconnected peers selected and also remove
  code which keeps track of last selected peer stats