Fix underscores and escaping in menu labels

[ztlxltl]

This PR fixes the display of underscores in the menu, especially for user-defined names, like database or tag names.

In GTK, an underscore in menu labels is used to mark the following letter as keyboard accelerator called a mnemonic. The letter appears underlined, or becomes underlined when pressing the Alt key. In case the user defines a database name or a tag name that includes an underscore, the underscore will not be shown in the menu. By using .replace("_", "__"), the underscore is escaped so it will appear in the menu. The same applies for bookmarked people with an underscore in their formatted name (e.g. many names in the royal92.ged).

While checking other custom strings in the menu, I also noticed that plugin names used in the Reports and Tools menus are not escaped using html.escape() or xml.sax.saxutils.escape. While I don't know a plugin name that requires this, devs of new plugins could have a hard time debugging the resulting error message.

I also saw that less thorough cleaning up of plugin IDs happens when handling "unsupported items" in ViewManager.build_plugin_menu(). I'm not sure what those unsupported items can be, but from my limited understanding their IDs have a similar risk of having invalid chars as the IDs of other plugins. I wasn't able to test this, so I would appreciate it if someone who has more knowledge of this part could have a closer look.

In summary, this PR does the following:

• Recent databases: add .replace("_", "__")
• Reports and Tools menus: add html.escape() and .replace("_", "__"))
  • For "unsupported" items: additionally add valid_action_name()
• Bookmarks: add .replace("_", "__")
• Tags: add .replace("_", "__"))

[Nick-Hall]

Did you intend this to target the gramps61 branch?

[ztlxltl]

I wasn't sure which version this bug should ideally be fixed in. I'm happy to change it if you prefer 6.1.