Multiple commits to ease reviewing, but should be squashed I think.

Motivation / Problem

When registering a command or alias in console, memory is manually allocated to store the data in global custom sorted linked lists. And we rely on OS to free this memory at exit.

Also, underscores are removed from commands/aliases names on registration, but each access needs to remove underscores to find them (and some were forgetting the removal, at least info_cmd). And names in list_cmds output didn't match names shown in help.

Description

std::string is used to store names, and alias command.
Custom sorted linked list is replaced with std::map enclosed inside a static struct.
Map key uses names without underscores, but commands/aliases themselves store the name with underscores for display.
Underscore removal is handled inside the accessors, so the caller doesn't have to care about it.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker