toaster: Add layer details page feature

toaster: Add layer details page feature

This commit adds the layer details page which shows the metadata for the
layer such as layer description, machines associated with the layer as well
as the targets provided.
If the layer is an imported layer this page also allows you to update
the layer's configuration.
>From this page you can add/remove the layer from the current project

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