Feature to change the tag layout

[n-peugnet]

There are 2 possibilities:

1. In the root config, rename layout variable into pagelayout and add taglayout.
2. Make tags use the same layout as pages.

Solution 2. requires the tag function to be changed to match the same variable as the page in the layout.
Solution 1. gives more freedom as one can still choose the same layout for both pages and tags.

With solution 1. I could still later make the variables of the tag layout to match the ones of the page layout so that both layouts are fully compatibles. Also, both page and tag could use the same replacement function.