util.dataforms: Add support for datetime field types via XEP-0122

mod_http_file_share: Move number coercion into util.dataforms

mod_admin_adhoc: Move number coercion into util.dataforms Internal use of XEP-0122 to shift the responsibility for converting numbers to strings.

ejabberd2prosody.lua: fix MUC subject conversion with appropriate destructuring

util.startup: Understand -h, -? as --help in prosodyctl but ignore prosodyctl -h showing an error was not very helpful, especially since prosodyctl shows its help for any unknown (or none) command.

util.startup: Show brief usage on `prosody -h|-?|--help` Seems more suitable than asking if prosodyctl was meant to be used, or going ahead and starting.

mod_c2s,etc: Identify stanza object with appropriate function Better than duck typing, in case anyone ever passes a non-stanza table with a 'name' field.

mod_s2s: Fix logging of <stream:error> consistency with other mods `reason` was often a table, so the log said "table: 0xptr" or such. mod_c2s, mod_bosh etc logs the stream error stanza object, so better do the same. It would be nicer if this was an util.error object, but that will have to be a future change.

util.startup: Skip config readability check in migrator (thanks eTaurus) This field is empty for reasons when invoked by prosody-migrator, which threw an error: > bad argument #1 to 'open' (string expected, got nil)

mod_http_file_share: Silence luacheck warning