Use correctly sized gravatars when possible

Provides a gravatar_fixup vmethod that accepts a pixel size to set on
gravatar URLs.  It also adjusts them to use HTTPS, replacing the
existing repeated templated code.
Merge pull request #1206 from haarg/gravatar-fixup

Use correctly sized gravatars when possible
Fixes Dist::Zilla search precision test.
Move plussers to right and limit - start of #1184
Merge pull request #1207 from CPAN-API/leo/less_plussers

Move plussers to right and limit number of icons
Munge more Gravatar urls into https submission

This is based on idly scanning
http://explorer.metacpan.org/#/693f90463a5e4980272a by hand.
Merge pull request #1208 from CPAN-API/tsibley/more-gravatar-munging

Munge more Gravatar urls into https submission
Adds note about pre-receive hook to CONTRIBUTING.md