Intorduction of line_attachment in presets

[francois.lacombe]

Dear maintainers,

The key line_attachment has been very recently reviewed on the wiki and received an approval vote.
​https://wiki.openstreetmap.org/wiki/Key:line_attachment

The post-vote cleanup is in progress and documentation is currently under completion.
It may be great to update JOSM presets as follow :

• Add the key with its four values on power supports presets power=tower, power=pole, power=insulator, power=portal and power=terminal
• Remove anchor and suspension as possible values for tower:type key in any context.
• Warn about the use of tower:type=anchor and encourage the replacement with line_attachment=anchor
• Warn about the use of tower:type=suspension and encourage the replacement with line_attachment=suspension
• Warn about the use of line_attachment on any other feature than a node.

Feel free to ask for any unclear point, all the best

François