SourceLayout: port config and select-loop priority polishing

SourceLayout: port config and select-loop priority polishing

- renames http_port_list to AnyP::PortCfg
- de-duplicate https_port_list into AnyP::PortCfg
- shuffles related globals and defines into anyp/PortCfg.*
- renames MAXHTTPPORTS to MAXTCPLISTENPORTS to suit its actual coverage of HTTP and HTTPS ports.
- shuffled config port clone function into a method.
- rename ICP/HTCP/SNMP API functions to consistent *OpenPorts() and *ClosePorts()

  NP:following applies to incoming_* and *_poll_cnt directives.
- renames *_icp_* to *_udp_*
- renames *_http_* to *_tcp_*
- shuffles duplicated struct SquidConf options into a shared structure
- shuffles related defines into comm/Loops.h
- documents options better

- various other cosmetic syntax tweaks and polish

One bug fix:
  comm_dns_incoming was not being propigated in StatsHist copy/clone.
  Now is. I seem to remember mention of something similar being zero before,
  but can't find the bug report.