Check and filter long Logo elements

[iay]

The upstream tooling has code to check the length of Logo elements. It introduces two thresholds.

• By default, any Logo longer than 50,000 characters is removed from the entity (the entity itself is not removed as a result of this) and logged.
• By default, any Logo longer than 40,000 characters (but not included in the above rule) is logged.

Once the upstream merge in #9 is completed, this will be available. We should add this to the eduGAIN import policy and to its wiki documentation.

[iay]

The page where we document the eduGAIN import policy has moved; we need to update the policy file to point to the new location:

https://spaces.at.internet2.edu/display/federation/Interfederation+Technical+Policy

In addition, the old "development" version of that page no longer appears to be present (or perhaps I just can't see it, I recall that it was not generally visible and perhaps there has been a permissions issue in the transfer). It will need to be recovered.

We don't appear to have a "warn but take no action" category in those rules, so we may need to insert one and renumber accordingly.

[iay]

There is no longer a development version of the technical policy page; changes need to be staged through a new mechanism. As such, we can't refer to that page in the source any more.

Tweaked that in commit 1149250 on the 13-logos topic branch.