Implement localize function to remove ghost cells of a given triangulation

[fverdugo]

Implement localize function to remove ghost cells of a given triangulation

[fverdugo]

trian_l = localize(trian_lg,part,cell_to_owner)

Compute a new triangulation trian_l that points only to locally owned cells, i.e.

all( cell_to_owner[ get_cell_id(trian_l) ] .== part ) #-> true 

from a given triangulation that (possibly) points to both owned and ghost cells.

It should be easy to implement using RestrictedTriangulation

[fverdugo]

Added function remove_ghost_cells and include_ghost_cells in commit 1be9a85

Addresses first item in issue #3

[fverdugo]

Functions remove_ghost_cells and include_ghost_cells still need to be extended to boundary and skeleton triangulations.

[amartinhuertas]

Functions remove_ghost_cells and include_ghost_cells still need to be extended to boundary and skeleton triangulations.

Done here for SkeletonTriangulation. For BoundaryTriangulation the include_ghost_cells for regular triangulations can be re-used as is.

However, in order to have fully working TriangulationPortion of BoundaryTriangulation and SkeletonTriangulation this PR is needed in Gridap.jl.