Document common populated places properties

[nvkelso]

When working with populated places theme I ensured each NEW record had the minimum properties:

• NE_ID - from Brooklyn Integers
• NAME - based on issue decision
• NAMEASCII - without any diacritical marks
• NAMEPAR - only when single other name in common usage
• NAMEALT - when appropriate, a list
• SCALERANK - look around at similarly sized cities in that map area
• NATSCALE - look around at similarly sized cities in that map area
• LABELRANK - look around at similarly sized cities in that map area
• FEATURECLA - based on issue decision or no change
• ADM0CAP - set to 1 if a country capital, else 0
• CAPIN - only if it's a country capital
• WORLDCITY - to 0 since those are controlled lists
• MEGACITY - to 0 since those are controlled lists
• SOV0NAME - based on what NE sov it falls in
• SOV_A3 - based on what NE sov it falls in
• ADM0NAME - based on what NE country it falls in
• ADM0_A3 - based on what NE country it falls in
• ADM1NAME - based on what NE admin1 it falls in, or it's real world value
• ISO_A2 - based on what NE country it falls in
• POP_MAX - these are needed to set townspot size and label text size, for "metro area"
• POP_MIN - these are needed to set townspot size and label text size, for "incorporated area"
• RANK_MAX - these are needed to set townspot size and label text size, formula
• RANK_MIN - these are needed to set townspot size and label text size, formula
• GEONAMEID - when available, sometimes listed in Wikidata page.
• TIMEZONE - see the NE theme but commonly avaialble
• MIN_ZOOM - look around at similarly sized cities in that map area
• WIKIDATAID - when available, sometimes listed in Wikidata page (eg https://www.wikidata.org/wiki/Q60)
• WOF_ID - when available from https://spelunker.whosonfirst.org/

NOTE: all the name_* localizations are picked up later by running the scripts in https://github.com/nvkelso/natural-earth-vector/tree/master/tools/wikidata.

See related work in #477 and #5 and #457.