Update the list of supported compilers

as decided in Berlin 2014.
Remove more references to SGrid from the grid Howto
Mention range based for in the howto

We cannot yet rewrite our code examples with
range based for, because gcc 4.4 and 4.5 do not
support it. But we can at least hint the reade towards it.
Change more occurences of SGrid -> YaspGrid
Briefly describe YaspGrids tensorproduct feature
Change code examples to use YaspGrid instead of Sgrid