You can now search for and load existing metadata

[marcpage]

%metadata_yaml% editor

There is an editor in the works, but does not currently work yet.
To run the editor:

1. Add webserver.yml next to genweb.yml
2. Execute python3 -m genweb.webserver
3. Point your browser at localhost:8000

Here are the current features of the non-functional editor:

• The metadata type selector should change the appropriate fields shown in the editor for the chosen type
• Clicking the 🔎 button next to the Identifier field will allow you to search and load existing metadata
• If the Identifier field is an existing metadata identifier, the submit button changes from Add to Update
• Clicking the 🔎 button next to the People field will reveal a people search
• Typing in the people search will filter the people ids
• Clicking on a person in the filter list will display the person and their family
• This will allow copy/pasting of people ids into the People field

Part of #36