Enable searching for levels by name on the mp create screen.
get_levels_by_type -> ..._unfiltered, get_filtered_levels_by_type ->
get_levels_by_type.

create_engine works on the filtered lists everywhere, so I made it
'default' here too. I didn't remove the unfiltered function because it
might be useful in some use cases.
Ignore case when filtering levels.
Return campaign names when campaign names are requested.

A copypaste error caused create_engine to return random map names.