In oomph-convert.py overwrite output file outdated
In oomph-convert.py clean up booleans and flag naming
Add broken virtual vertex_node_pt(..) to FiniteElement

It's implemented by both T and Q elements so it makes sense to be able
to call it using pointers to the base class!
Add function to create mesh boundary node lookups from the nodes

Since the nodes themselves already store data on which boundary(s) they
are on we can build the mesh's lookup schemes from the node data.

This makes life much simpler when using old meshes to create the nodes
for new meshes.

Only takes O(Nnode) time (unlike some of the other boundary lookup
initialisation functions).