invalid CSS IDs in admin menu

[oaoao]

CSS IDs are being partially normalized in the admin menu. however, plugins that use URLs such as

directory/file.php

are giving CSS selectors such as:

id="toplevel_page_directory/file"

slashes are not valid, and should be converted to - or _. this bug is currently breaking styling.

[azaozz]

(In [10123]) Filter menu IDs, fixes #8523

[vladimir_kolesnikov]

Replaces '/' with ':' in element IDs

[oaoao]

vladimir-- ":" is valid, but is not a good idea due to selectors.