Several things going on here:
1) refactor `get_display_string()` to `get_display_name()` to be more precise
2) likewise, refactor `alt_name` to `display_name`
3) automatically generate display names when parsing the ship, ship class, and weapon class for the first time
4) remove the on-the-fly truncation of names with hash symbols
Basically this subsumes the `end_string_at_first_hash_symbol` logic into the display name. Rather than truncate the name every time it's displayed, truncate it once when it's parsed. This takes advantage of the previous display name infrastructure, since display names are a superset of the case of truncating the hash symbol.
This also has the benefit of now allowing hash symbols within display names. When updating Destiny of Peace, I noticed that "Lockheed Shuttle #4" would no longer display properly; and it was not previously possible to fix this even with display names.
I could pull out the `get_display_string()` and `alt_name` renaming into a separate PR if desired.
For quite some time missions have had the ability to edit more than one background. This was previously used for fallback loading in case the first background's bitmaps were not available, but I realized it would be very handy to allow switching between backgrounds for in-mission jumps.
The FRED background dialog can now add and remove backgrounds from the list. Additionally, a new `change-background` sexp can instantly switch between backgrounds without messing around with bitmap references.
Fabian Woltermann