WIP: Include "child" assets in inventory email and other views

[marcusmoore]

Here is the set up for the description that follows:

• asset-001, asset-002, asset-003, and asset-004 are checked out directly to the user
• asset-001-01 is checked out to asset-001
• asset-003-01 is checked out to asset-003
• asset-003-02 is checked out to asset-003
• "Show assets assigned to assets" is enabled in settings
  

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As pointed out in #16811, #13479 the email that is sent when clicking the "Email list of all Assigned" button does not include "child" assets (assets that are checked out to the assets checked out to the given user):

But they are included in the view for "Printing All Assigned":

Helpfully they are numbered x.x

This PR addresses that by including the child assets in the email along with the x.x numbering:

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In addition, I noticed that child assets were missing when viewing a user's assets (/users/1#asset) or your own asset's (/account/view-assets#assets).

I've add this to your viewing your own assets:
Before:

After:

• And the last thing to do is add it to viewing a user's assets:
  Before:
  

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fixes #13479

[swift2512]

@snipe @marcusmoore it's nice to see that it's finally coming to Snipe-IT. While you are working on 'Child assets' please consider adding 'Child accessories' to the views.

Assets can have various items checked-out to it. For example, you could check-out DSLR camera that has various 'assets' (LENSE, FLASH, TRIPOD) and 'accessories' (memory card, strap, filter) checked-out to it and user could see a full list of items.
Users and managers (admins) should be able to see all this in: 'Account view', 'Print All Assigned' and check-in/check-out emails sent to users. I have a feeling that it's nearly impossible to make 'Child' Accessories appear under Assets view (view-assets#assets) so subtle hints like exclamation marks in asset list and banners in user account panel (E.g., 'Your Assets have other items checked-out to it. You can view full list via 'Print All Assigned' or 'Email List of All Assigned.') This would be helpful in cases where person has to sign/confirm (enabled acceptance) for received assets. Now user only signs for parent asset and list of 'child items' is completely hidden.

[marcusmoore]

@swift2512 that makes sense to me. It might not be included in this but can be addressed in the future.