[Feature] Add command 'Copy URL' in Submodule context menu

[goran-w]

Suggestion: Add new command Copy URL in Submodule context menu. This would be consistent with the existing Copy Relative Path command, and just as useful (for example, if we find we need to set up the same submodule URL in another repo).

See also #1522. NOTE: If this becomes too crowded, move the Copy-commands into sub-menu 'Copy'.

[love-linger]

Done

[goran-w]

Thanks!