[feature] Set default header and avatar for API accounts to GtS ones (#799)

* validate web-asset-base-dir

* move default icons into converter

* always ensure avatar + header on api accounts

* update tests

* add default header

* don't return error from web module creation anymore

* tidy a bit

* use pngs for default avatars rather than svgs

internal/typeutils/internaltofrontend.go

@@ -190,6 +190,9 @@ func (c *converter) AccountToAPIAccountPublic(ctx context.Context, a *gtsmodel.A
 		Suspended:      suspended,
 	}
 
+	c.ensureAvatar(accountFrontend)
+	c.ensureHeader(accountFrontend)
+
 	return accountFrontend, nil
 }