Implement vertex reordering during graph copy
Implemet __copy__ in Graph and PropertyMap
Implement weighted degree property maps and weighted degree selectors
Do not use filter stash internally, in favour of graph views
Get rid of the filter stash in Graph class

Fully remove the filter stash and associated functions in the Graph
class, in favor of using GraphView uniquely.
Remove old documentation from filter stash operations
Fix edge() function in adj_list class
Implement optional faster O(1) removal of edges
Make alias Sampler default-constructible
Change OpenMP schedule directive to 'static' instead of 'dynamic'

Use schedule(static, 100), to reduce overhead with small graphs in the
majority of cases.