Add boldfaced "Key" title in the table footer when %key is used

[anermina]

According to ISO's guidelines given in metanorma/mn-samples-iso#96 (comment) regarding the key element in the table footer, the key section should be preceded by a “Key” title in bold, as shown in the example below.

Currently, Metanorma generates the key section as below

when the following markup is used.

NOTE: Ce tableau est basé sur l'<<ISO7301,table=1>>.

NOTE: Certains contrats commerciaux peuvent exiger des complémentaires à celles fournies dans le présent tableau.

NOTE: Seul le riz (cargo) rouge entièrement décortiqué est pris en considération dans le présent tableau.

[%key]
N/A:: N'est pas applicable.

[opoudjis]

To move table key around properly in Word postprocessing, which is not currently happening, need to wrap it in div[@class = 'figdl'], treating it the same as figure keys are already being treated.

[opoudjis]

I'm marking up this key title as the title of a definition list, which is ListTitle; but ListTitle is centered, and this Key title is not. Ugh. Will override in postprocessing for definition list titles which are table keys.

[opoudjis]

Need to keep definition list, preceding title paragraph and following notes together in a div in rendering in HTML and DOC output, since they are going to be treated as a unit.

[opoudjis]

Will finish tomorrow

[opoudjis]

Extend the wrapping in div to ol and ul. Disruptive change, but future-proofs list rendering.