Release v0.4

First release in a long time :).

User-facing changes:

• Add /apiblock <pos> delete header <name>. This allows for actually deleting headers.
• Disable API block polling (sending requests) when the route is empty or blank.

Internal changes:

• Address security vulnerability by updating org.apache.httpcomponents.client5 to v5.6.1
• Refactor and remove redundant fields in APIBlockEntity.
• Tighten privacy on APIUpdater fields.