fix: history rows show the ISO datetime and the age (closes #760)

Home, AddressDetail and AddressToken showed only the relative age, with
the datetime as a tooltip. Each row now shows the datetime and then the
age in parentheses, on a line of its own, through transactionTimeHtml()
in helpers.js, which TransactionDetail also uses. The direction label
moves to its own right-aligned line below. README.md and docs/README.md
describe the new row.

Model: opus-5-5

docs/README.md

@@ -415,9 +415,10 @@ the setting is off, each history list shows one line saying so.
 
 Each row shows:
 
-- the age and the direction, "Sent" or "Received". A transaction can also ask a
-  contract to do something; that is a contract call. A row for a contract call
-  shows the call's name instead, such as "Approve" or "Swap";
+- the time, as a date and time and as an age;
+- the direction, "Sent" or "Received", on the line below. A transaction can also
+  ask a contract to do something; that is a contract call. A row for a contract
+  call shows the call's name instead, such as "Approve" or "Swap";
 - the amount. A contract call row shows an amount only when the call moved a
   token. A swap row shows the amount received, or the amount paid in when no
   token came back. A row with no amount shows only a symbol, such as `USDC` or