feat: label interpolation in the going

...http..mathhub.info/FrameIT/frameworld/$Angle$Sum.omdoc.xz

...mathhub.info/FrameIT/frameworld/$Frameworld$Meta.omdoc.xz

...athhub.info/FrameIT/frameworld/$Meta$Annotations.omdoc.xz

...p..mathhub.info/FrameIT/frameworld/$Opposite$Len.omdoc.xz

...ttp..mathhub.info/FrameIT/frameworld/$Pythagoras.omdoc.xz

...eIT/frameworld/$Triangle$Scroll_$General$Problem.omdoc.xz

...rameworld/$Triangle$Scroll_$Right$Angled$Problem.omdoc.xz

...eworld/integrationtests/$Sample$Situation$Theory.omdoc.xz

errors/mmt-omdoc/MetaTheories.mmt.err

errors/mmt-omdoc/Scrolls/TriangleScrolls.mmt.err

narration/IntegrationTests/SituationTheory.omdoc

narration/MetaTheories.omdoc

narration/Scrolls/TriangleScrolls.omdoc

relational/Scrolls/TriangleScrolls.rel

...onal/http..mathhub.info/FrameIT/frameworld/$Angle$Sum.rel

...tp..mathhub.info/FrameIT/frameworld/$Meta$Annotations.rel

...l/http..mathhub.info/FrameIT/frameworld/$Opposite$Len.rel

...nal/http..mathhub.info/FrameIT/frameworld/$Pythagoras.rel

.../frameworld/integrationtests/$Sample$Situation$Theory.rel

source/IntegrationTests/SituationTheory.mmt