Various issues/typos

[axcore]

I noticed a few issues, in case you ever feel like doing a new release.

• In nodes-feldweg.lua, there are four modes, but at the top of the file "flat" is checked twice and "simple" is not checked
• In several nodes in that file, and in a few other files, "groups" appears twice, looks like a typo
• Also at line 132, "groups" has been mistyped as "roups"
• Also at line 130 there's a texture "cottages_feldweg_orig.png" that doesnt' exist
• In nodes_furniture.lua, in player messages, "comfortable" has been misspelled several times
• In cottages:sleeping_mat, there are two selection box fields
• The text at the top of some formspecs is only partially visible