Remove old unused build reports page
Expose build reports in the feature API
Fix build report parser

This adds an explicit distinction between required and optional fields,
so we don't get an error if the latter are missing.

Closes #226.
Add build log retrieval to reports feature API
Implement build reports view
Give tables a bit of wiggle room
Add extra goodies to build report type

The build report structure gains two fields:

* A time stamp;

* Documentation builder flag, which is True iff the client was
  generating documentation for upload.

In addition, solver failure is added to the list of install outcomes.

This only changes the types and migration machinery; front-end support
will come in a later commit.

The existing migration code (commit 111f3897) has also been removed; I
couldn't make it fit with the new changes. As the former is quite old
(Nov 2013), the removal shouldn't be too worrying.
Add timestamp to build report view
Affix a timestamp to every submitted report
Add queryPackageReports
Add build status indicator to package front page
Only allow doc builder flag when user can upload docs
Build client: add doc builder flag to submitted reports
Fix build report text view

This should return a properly formatted report, not an internal dump.
Merge pull request #240 from lfairy/build-reports

Implement build reports view and status indicator
Converted serveTarball to use the useETag helper.

ServeTarball deals with serving individual files from a package's tar file.

The previous code handled ETags by hand, and would include them
in the response but ignore any ETags in the request header.