database: add helpers to fetch all columns

The current solution of fetching columns based on the GraphQL context
has some limits. While probably not the solution for all use-cases, it
sometimes can be desirable to simply fetch all columns from the database
when retrieving objects.

This commit adds two simple functions doing just that. They can be used
when building SQL queries, like

    query := database.SelectAll(new(model.Email))

and

    rows.Scan(database.ScanAll(&email)...)

database: Remove Apply

database: always include table name in SELECT

When JOINs are performed on the auto-generated SELECT query,
multiple tables may have the same field names. For instance, in
lists.sr.ht the "list" and "subscription" tables both have an "id"
column. When performing a "mailingLists" GraphQL query this results
in this error:

    pq: column reference "id" is ambiguous

The old query looks like this:

    SELECT "description", "name", "id", "owner_id", "updated", COALESCE(
    access.permissions,
    CASE WHEN list.owner_id = $1
    THEN $2
    ELSE CASE WHEN sub.id IS NOT NULL
    	THEN list.subscriber_permissions
    	ELSE null END
    END,
    list.nonsubscriber_permissions | list.account_permissions), access.id AS access_id, sub.id AS subscription_id FROM list LEFT JOIN access ON
    access.list_id = list.id AND
    access.user_id = $3 LEFT JOIN subscription sub ON
    sub.list_id = list.id AND
    sub.user_id = $4 WHERE list.owner_id = $5 ORDER BY "updated" DESC LIMIT 26

The new query looks like this:

    SELECT "description", "name", "list"."id", "list"."owner_id", "list"."updated", COALESCE(
    access.permissions,
    CASE WHEN list.owner_id = $1
    THEN $2
    ELSE CASE WHEN sub.id IS NOT NULL
    	THEN list.subscriber_permissions
    	ELSE null END
    END,
    list.nonsubscriber_permissions | list.account_permissions), access.id AS access_id, sub.id AS subscription_id FROM list LEFT JOIN access ON
    access.list_id = list.id AND
    access.user_id = $3 LEFT JOIN subscription sub ON
    sub.list_id = list.id AND
    sub.user_id = $4 WHERE list.owner_id = $5 ORDER BY "updated" DESC LIMIT 26

database: panic on errors from Commit/Rollback

The previous change would eat the error from fn(tx); in truth we should
ensure that it is returned to the caller. This panics instead if an
error occurs during Commit or Rollback. I'm not sure of what scenarios
would cause this to occur, but they all probably deserve further
investigation - a panic will raise it to our attention.

database: handle Commit/Rollback errors

database: expand field map for composite fields

This allows models to fetch multiple SQL columns to obtain the data
necessary to compute a single composite GraphQL field, while still
avoiding unnecessary fetches if those fields are not queried.

database.Apply: add support for non-pointer fields

database.WithTx: rollback if func returns error

Previously, this only rolled back if the called function panicked. This
updates it to also roll back if the called function returns an error.

Add legacy webhooks worker implementation

Expand context for work queues

Add basic auth tests

Import GQL server interfaces from gql.sr.ht