Generating PVD files when the Triangulation is not present on all Ranks

With the current implementation, we can not generate the paraview files when the triangulations are not present on all MPI ranks. In issue #70, this has been written as a #TODO task for taking nothing.

Since I needed this functionality for my use case, I tried to fix it myself, but I had to use functions from Mpi.jl as well. Below are the changes I made to make it work.

```
struct DistributedPvd{T<:AbstractArray}
pvds::T
main_rank::Int
end

function Visualization.createpvd(trian::DistributedTriangulation,parts::AbstractArray,args...;kwargs...)
main_rank = -1
map(local_views(trian), parts) do LocTrian, part
flag = part * !(num_cells(LocTrian) == 0)
global_flag = Vector{Int}(undef, MPI.Comm_size(MPI.COMM_WORLD))
MPI.Allgather!([flag], global_flag, MPI.COMM_WORLD)
main_rank = maximum(global_flag)
end
pvds = map_main(parts,main = main_rank) do part
p = paraview_collection(args...;kwargs...)
end
DistributedPvd(pvds,main_rank)
end

function Visualization.createpvd(f,trian::DistributedTriangulation,parts::AbstractArray,args...;kwargs...)
pvd = createpvd(trian,parts,args...;kwargs...)
try
f(pvd)
finally
savepvd(pvd)
end
end

function Visualization.createpvd(parts::AbstractArray,args...;kwargs...)
pvds = map_main(parts, main = 1) do part
p = paraview_collection(args...;kwargs...)
end
DistributedPvd(pvds,1)
end

function Visualization.createpvd(f,parts::AbstractArray,args...;kwargs...)
pvd = createpvd(parts,args...;kwargs...)
try
f(pvd)
finally
savepvd(pvd)
end
end

function Visualization.savepvd(pvd::DistributedPvd)
map_main(pvd.pvds, main = pvd.main_rank) do pvd
vtk_save(pvd)
end
end

function Base.setindex!(pvd::DistributedPvd,pvtk::AbstractArray,time::Real)

map(pvtk) do pvtk
if !isnothing(pvtk)
vtk_save(pvtk)
end
end

map_main(pvtk,pvd.pvds,main = pvd.main_rank) do pvtk,pvd
pvd[time] = pvtk
end
end
```