Map loading should consider tag 0 as a valid tag and add its respective entries just like the rest of tags.

P_SpawnSpecials() line special spawn sequence now uses the taglist, until we move on to using args[0].

Replace most P_FindSpecialLineFromTag() cases with Tag_FindLineSpecial(), which settle with the first found result.

Replaces P_FindSectorFromTag() occurrences with its corresponding macro and vanishes it from existence.

Remove faulty code from T_MovePlane()

See merge request !876

Remove the disabled/broken bridge thinker code

See merge request !879

Actually remove the entire code block in T_MovePlane(), and remove line_t.tagline as it served no other purpose.