Create a Metabase backwards-compatibility shim API

[preaction]

While we transition away from the Metabase project to a simpler way of storing raw reports, we will need a backwards-compatible way for existing clients to still submit reports. This API should write directly to the local CPAN Testers cache of the Metabase for the time being, until we figure out that simpler way of storing raw reports.

This shim API should function as a Metabase::Gateway by mimicking the REST API provided by Metabase::Web.

It must be able to:

• [x] Submit new reports to the Metabase
• [x] Update existing reports(?)
  • I'm not sure if this is a required feature or not. CPAN::Testers::Data::Generator seems to say that reports may be updated after-the-fact, but it might just be worried about reports submitted out-of-order because Amazon SimpleDB has no good date-based query methods
• [x] Expose a /tail/log.txt with a text log of the last 1000 reports
  • This is a backwards-compatibility API for http://fast-matrix.cpantesters.org
  • The format should be:
    • [2017-03-05T21:54:51Z] [Chris Williams (BINGOS)] [pass] [PLICEASE/Alien-Build-0.19.tar.gz] [x86_64-gnukfreebsd] [perl-v5.14.0] [5c074038-01ee-11e7-a074-e1beba07c9dd] [2017-03-05T21:54:51Z]
    • [<updated time in ISO8601>] [<tester from>] [<grade>] [<distfile>] [<archname>] [<perl version>] [<guid>] [<created time in ISO8601>]
      • This file was created by https://github.com/cpan-testers/cpantesters-api/blob/metabase-api/eg/legacy/tail-recent-reports.pl

When a report is submitted directly to the local cache, it will have a GUID, but not an ID (which gets added when the report is parsed into the cpanstats table by CPAN::Testers::Data::Generator). In order for this new shim API to work, we will need to alter CPAN::Testers::Data::Generator by:

• Allowing the id field in the metabase table to be NULL
• Making the generate method of CPAN::Testers::Data::Generator determine the work it needs to do by selecting all the rows in the metabase where the id field is NULL
• Making the generate method of CPAN::Testers::Data::Generator update the id field of the metabase table with the correct ID generated by inserting into the cpanstats table

This is the main API to submitting reports, so it is important that it is as robust as possible. All care should be taken that it does not go down, and it should be tested thoroughly before being put into production.

[preaction]

This work is started on the metabase-api branch. The initial metabase shim API for submitting new reports is complete, but must be tested against live clients.

[preaction]

We also need to create a basic web page that indicates what this site is and that users should use different APIs for this...

• [x] Add welcome landing page to direct users to another place

[preaction]

This is done enough for a public beta at http://metabase-beta.cpantesters.org. Any future problems in testing will be resolved in individual tickets.