Each evaluation registration produces a list of new jobs. Until now, only the
jobs which build outputs were not stored in the "Outputs" table were added to
the "Builds" table.

It means that Cuirass looses track of the job list associated to a given
evaluation.  This is problematic to provide the overall build status of an
evaluation or to find the evaluation providing the best build coverage.

Add a new "Jobs" table that stores the job list of each evaluation.  Also add
a new "/api/jobs" API to consult it.

* src/sql/upgrade-2.sql: New file.
* Makefile.am (dist_sql_DATA): Add it.
* src/schema.sql (Jobs): New table.
* src/cuirass/database.scm (db-add-job, db-get-jobs): New procedures.
(db-register-builds): Call db-add-job.
* src/cuirass/http.scm (url-handler): New "/api/jobs" route.
* tests/database.scm ("db-get-jobs", "db-get-jobs names"): New tests.
* doc/cuirass.texi (Web API, Database): Document it.

* src/static/css/cuirass.css (.content): Remove horizontal padding.

* src/cuirass/templates.scm (html-page): Add a footer.
* src/static/css/cuirass.css (body, footer): New sections.

* src/cuirass/http (respond-gzipped-file): Rename it to ...
(respond-compressed-file): ... this new procedure. Add support for bzip2
compressed files.
(url-handler): Adapt it.

* src/cuirass/base.scm (handle-build-event): Add a store argument and use it
to record the log file.
(spawn-builds): Adapt it.

* src/cuirass/base.scm (set-build-successful!): Remove log argument.

* src/static/css/cuirass.css (#search): Set z-index to 1.

When a new evaluation is triggered by a single channel update, the
matching specification can have other channels that are not updated. In that
case, "db-get-checkouts" will only return the checkout corresponding to the
channel update.

This cause "channel-instances->profile" to fail this way:

In guix/channels.scm:
   911:32  3 (channel-instances->derivation _)
   871:36  2 (channel-instances->manifest (#<<channel-instance> cha?>))
    759:6  1 (channel-instance-derivations (#<<channel-instance> ch?>))
In ice-9/boot-9.scm:
  1669:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1669:16: In procedure raise-exception:
ERROR:
  1. &message: "'guix' channel is lacking"
  2. &fix-hint: "Make sure your list of channels\ncontains one channel named @code{guix} providing the core of Guix."
  3. &error-location: #<<location> file: "guix/channels.scm" line: 557 column: 18>

Introduce a db-get-latest-checkout procedure that returns the last checkout of
a given channel. Use it to request the checkouts of all the channels before
creating the profile.

* src/cuirass/database.scm (db-get-latest-checkout): New procedure.
* tests/database.scm ("db-get-latest-checkout"): New test.
* src/cuirass/scripts/evaluate.scm (latest-checkouts): New procedure.
(cuirass-evaluate): Use it.

* configure.ac: Add Guile module check.

This is superseeded by the notification system.

* doc/cuirass.texi (Specification): Document the channels build type.

* src/cuirass/specification.scm (%build-types): Add 'channels support.