Merge pull request #696 from openspending/672-ssl-for-openspending

672 ssl for openspending
Dataset index caching and pagination.

This fixes #655 in issue tracker on github.
This fixes #642 in issue tracker on github.
Merge pull request #699 from openspending/642-dataset-index-cache

Dataset index caching and pagination.
Removed invalidation that was used for testing purposes.
Merge pull request #700 from openspending/642-dataset-index-cache

Removed invalidation that was used for testing purposes.
Switch to assets.okfn.org's cloudfront to piggyback on the ssl license
Switch host of twitter and feed icons to use our new cloudfront
Merge remote-tracking branch 'origin/master' into 672-ssl-for-openspending