construct PhylogeneticTree from graph

[antonydellavecchia]

Creating a phylogenetic tree from a directed graph.

Keeps track of the permutation of the vertex ordering so that user can work with the same vertices without iknowing about the underlying polymake vertex ordering.

Labelings work as expected by using the label :leaves for the leaf nodes and :distance for the edges

[fingolfin]

Tests fail:

      From worker 2:	Phylogenetic Trees: Error During Test at /Users/oscarci-tester/oscar-runners/oscar-runner-03/_work/Oscar.jl/Oscar.jl/test/Combinatorics/PhylogeneticTrees.jl:1
      From worker 2:	  Got exception outside of a @test
      From worker 2:	  MethodError: no method matching Oscar.PhylogeneticTree{Float64}(::Polymake.LibPolymake.BigObjectAllocated)
      From worker 2:	  
      From worker 2:	  Closest candidates are:
      From worker 2:	    (::Type{Oscar.PhylogeneticTree{T}} where T<:Union{Float64, QQFieldElem})(::Any, ::Any)
      From worker 2:	     @ Oscar ~/oscar-runners/oscar-runner-03/_work/Oscar.jl/Oscar.jl/src/Combinatorics/PhylogeneticTrees.jl:2
      From worker 2:	  
      From worker 2:	  Stacktrace:
      From worker 2:	    [1] tropical_median_consensus(arr::Vector{Oscar.PhylogeneticTree{Float64}})
      From worker 2:	      @ Oscar ~/oscar-runners/oscar-runner-03/_work/Oscar.jl/Oscar.jl/src/Combinatorics/PhylogeneticTrees.jl:286
      From worker 2:	    [2] tropical_median_consensus(::Oscar.PhylogeneticTree{Float64}, ::Oscar.PhylogeneticTree{Float64})
      From worker 2:	      @ Oscar ~/oscar-runners/oscar-runner-03/_work/Oscar.jl/Oscar.jl/src/Combinatorics/PhylogeneticTrees.jl:314
      From worker 2:	    [3] macro expansion
      From worker 2:	      @ ~/oscar-runners/oscar-runner-03/_work/Oscar.jl/Oscar.jl/test/Combinatorics/PhylogeneticTrees.jl:8 [inlined]

[benlorenz]

This needs some further discussion as the current design could contradict what polymake expects for the PhylogeneticTree object.