bug when multiple use of item.html.twig

Data-Manager is a great plugin for developing.!!! But it fails if used too often.

# Briefly my problem
- I have written two plugins, one customises the `type` list, called here `var-dumper`, the other customises the `type` details, called `content-edit`.
- However, when I enable `var-dumper`, which customises `type` **list**, the customised `type` **detail** for the other plugin disappears.
- Two `types` (using the terminology of **DataManager**) are involved.

# In more detail
- I have reduced the files to the bare minimum that causes the problem, so only the Admin part is in each plugin.
- I include the pared-done php files, the data-manager twig files, and two data files in the expected format for each plugin.
- When `var-dumper` is not enabled, then the file in the `data/content-edit` directory is rendered as customised.
- When `var-dumper` is enabled, the same file is rendered by **data-manager** as if it is a non-customised `*.yaml` file.

Unless I have missed something, it seems there maybe a bug in **data-manager** when multiple non-standard datatypes are defined.

[data-man-test.zip](https://github.com/getgrav/grav-plugin-data-manager/files/2216063/data-man-test.zip)

Update: If the priority on enabling the `onPluginsInitialized` is changed from 0 to 100, then this will affect which plugin over-rides which. I'm not sure which plugin comes first when both are on the same priority. But after editing `var-dumper` I had to increase its priority to 100, and then found that its items.html.twig was not being used.