make mods global

Since splitting the game many people, especially newbies, have problems to install mods. When mods are used for every game it doesnt have to be stored (and updated) multiple times.

To disable mods players can use the gui then.
New textures for main menu

-different logo(-text)
-menusplash.png added (dirt-with-grass and lightsport in middle)
Revert "New textures for main menu"

This reverts commit f39a3ba52bf763840ddff23b1cb7dbb6447dc0cf.
Update wiki url
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' of https://github.com/BlockMen/minetest