Enhancement: Add a button to open a mail client with the URI in the mail body to the share sidebar.

[ghost]

Prompted by a discussion on IRC #osm-gb it would be useful for collectors and contributors of data if, having created a share marker, they could simply mail that URl with a simple button click. I know this only save a couple of button clicks (including a copy & past of the URI) but this would. possibly, encourage users to use share rather than adding bogus notes to the map.