Add line_management to power support presets

[francois.lacombe]

Dear maintainers,

The key line_management has been very recently reviewed on the wiki and received an approval vote.
​​https://wiki.openstreetmap.org/wiki/Key:line_management
It allows to better describe all power supports and remove any use tower:type or pole:type

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 seven values on power supports presets power=tower, power=pole, power=insulator, power=portal and power=terminal
• Warn about power:type or pole:type on any power support object since no value remains recommended with them. Encourage replacement as follows : ​https://wiki.openstreetmap.org/wiki/Proposed_features/Lines_management#Values_to_be_replaced
• Warn about the use of line_management on any other feature than a node.

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

François