In order to generate data for commit e0312dcf (types: Add resource label
events, 2019-07-16, v0.1200.1~1^2~1) a label was added to our sample
issue.  Fetch updated data for the issue and revise expected values.

Projects gained a field indicating whether they have an empty repo.
Issues gained a field indicating whether there is an empty task list.

Issues and MRs also gained a field for task completion, but we leave
that unimplemented for now.

Teach `data/fetch_from_gitlab.py` to save the JSON documents with
human-readable formatting and in sorted order.  Use `jq -S .` to format
our existing data the same way.  Formatted JSON documents are still
sufficient to test our crate's deserialization of them and will make
updates to new GitLab versions much more readable.

While at it, also teach the script to remove the user identities,
which we previously did by hand on each update.

Issues gained a field for the number of merge requests referencing them.
Merge requests gained a field for the current user's access.

Issues gained a field for who closed them.  Projects gained a field
for their merge method.

Issues and merge requests gained `discussion_locked` fields.
Issues gained a `closed_at` field.
Repo commit detail gained a `last_pipeline` field.

Issues and merge requests gained `time_stats` fields.
Projects gained a `resolve_outdated_diff_discussions` field.
Users restored the `theme_id` field, but it is now optional.

Issues and projects gained a `_links` field containing URLs of related
APIs (see gitlab-ce MR 10491, commit v9.5.0-rc1~301^2).  We model it
but do not expose it publicly since our clients won't need it.

Notes gained a `noteable_iid` when attached to issues and merge
requests (see gitlab-ce MR 13265, commit v9.5.0-rc1~14^2).

Fetch api v4 sample data from a GitLab 9.2 instance.  Using that and
GitLab sources `doc/api/v3_to_v4.md` and `lib/api/entities.rb`, update
our types accordingly.  Most changes are to rename "builds" to "jobs" or
"pipelines".

Also add strong types to internal ids in preparation for switching to
them when constructing API endpoints.