Move connectionset from analyzer and protocols from synthesizer

[elazarg]

Reopening #8.

Main differences from the version in the synthesizer:

• Remove mutating methods, replace with convenience constructors: All(), None(), TCPorUDPConnection(), ICMPConnection()
• Remove AllowAll field
• Dedicated StatefulState type
• Use netp.ProtocolString instead of ProtocolStr
• switchSrcDstPortsOnTCP() only actually switch dimensions when they differ
• Sort protocol strings lexicographically on output: ICMP,TCP,UDP
• Rename:
  • ConnectionSet => Set
  • getProtocolStr() => protocolStringFromCode()
  • getDimensionDomain() => entireDimension()
  • AllowAll => IsAll()
  • Intersection() => Intersect()
  • ConnWithStatefulness() => WithStatefulness()
  • getDimensionStr() => getDimensionString()
  • Except() => ExceptCidrs()

[elazarg]

I realized that the dimension types encode the order of the dimensions, which makes it harder to know what depends on the order of the dimensions, and contradicts the comment preceding dimensionsList:

// this should be the only place where the order is hard-coded

So the last commit changes the type of Dimension from int to string; the index of each dimension in a cube is looked up in the slice dimensionsList. It also delegates most of the work of swapping dimensions to the underlying hypercube set.