[Feat] v.random option to not prefix source column names

[marisn]

Current implementation of v.random adds a map name as a prefix to every original column name if attribute table is transferred. This solves the problem of duplicate column names but can lead to really long column names if input map name is long. There should be a flag to disable prefixing column names at all. The solution should handle duplicate column names by assigning a prefix only to the colliding names (most likely "cat" -> "_cat").