First stab at updating the CHANGELOG for 2.0

Probably more to do here..
CHANGELOG tweaks suggested in pr
Add some more stuff to the changelog
[#795] Fix and deprecate model.Package.is_private
[#795] Fix template to use correct attribute
[#795] Minor cleanup of import in model.package
prettifying ValidationErrors makes them less useful
[#787] Adds max-width to inner image to prevent 100% width in IE10
[#869] Validate that the user exists in _group_or_org_member_create
[#839] Add basic documentation for stats extension
[#746] Extend Pylons installer to tweak deployment.ini_tmpl

With the new 'paste.app_install' entry point on setup.py, we can define
a custom "installer" that basically allows us to define new variables to
be used on the deployment.ini_tmpl file. This is useful eg for defining
the ckan version and provide a link to the relevant documentation for
the configuration options.
[#746] Document datastore db url config options

And include them from the datastore setup documentation to avoid
duplication.
[#746] Update configuration.rst

* Document ckan.email_notifications_since
* Remove duplicate search.facet.limits
* Minor formatting tweaks
[#746] Document file store options in configuration.rst

TODO: Expand them
[#746] Update deployment.ini_tmpl

Remove legacy  and unused options, add new ones. Change the structure to
follow more closely the documentation on configuration.rst. Remove all inline
comments to avoid having documentation in more than one place.
Add note about ckanext.stats.cache_enabled
[#746] No : at end of sentence.
[#746] Edit a docstring in deployment.ini_tmpl

Minor edits
[#746] Minor edits to configuration docs
Merge branch '787-ie10-media-item-image-height'