toaster: add build dashboard buttons to edit/create custom images

toaster: add build dashboard buttons to edit/create custom images

When a build is viewed in the dashboard, enable users to edit
a custom image which was built during that build, and/or create
a new custom image based on one of the image recipes built during
the build.

Add methods to the Build model to enable querying for the
set of image recipes built during a build.

Add buttons to the dashboard, with the "Edit custom image"
button opening a basic modal for now. The "New custom image"
button opens the existing new custom image modal, but is modified
to show a list of images available as a base for a new custom image.

Add a new function to the new custom image modal's script which
enables multiple potential custom images to be shown as radio
buttons in the dialog (if there is more than 1). Modify existing
code to use this new function.

Add a template filter which allows the queryset of recipes for
a build to be available to client-side scripts, and from there
be used to populate the new custom image modal.

[YOCTO #9123]

Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Michael Wood <michael.g.wood@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>