Refactor of standoc

[opoudjis]

• Model part of standard in bibdata as extent: part 1 etc.
• Move structuredident to standoc as generic element of standoc
• Populate stucturedident for all flavours
• ~Populate stage with abbreviations and not the ISO numerals throughout~
• ~Move abstract, acknowledgement, foreword, introduction as general prefatory sections to all of standoc~
• ~Add type of clause, capture heading type as type of clause, impose enum~
• ~Add relatedTerm to terms~
• ~Add grammar to terms~

[opoudjis]

• Move abstract, acknowledgement, foreword, introduction as general prefatory sections to all of standoc

Done in https://github.com/metanorma/metanorma-standoc/issues/203

[opoudjis]

• Add type of clause, capture heading type as type of clause, impose enum

Done in https://github.com/metanorma/isodoc/issues/171

[opoudjis]

• Populate stage with abbreviations and not the ISO numerals throughout

Done in https://github.com/metanorma/metanorma-iso/issues/342

[opoudjis]

Related term and grammar added in https://github.com/metanorma/metanorma-standoc/issues/255

[opoudjis]

Model part of standard in bibdata as extent: part 1 etc.

... We could do that, but I don't now think we should: Parts are routinely published as completely different documents, with different identifiers; effacing their differences as extents, as if they are chapters of a monograph, would be misleading.

[opoudjis]

Move structuredident to standoc as generic element of standoc Populate stucturedident for all flavours

... No, don't think that's necessary.