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
[#869] Validate that the user exists in _group_or_org_member_create
[#839] Add basic documentation for stats extension
Add note about ckanext.stats.cache_enabled
[#839] Make clear what the different between the stats extension and the page tracking feature are, improve style.
[#839] Add link to stats extension from extensions docs
Merge remote-tracking branch 'okfn/master' into 839-stats-doc

Conflicts:
	doc/extensions.rst
[#839] Make the docs sound better
[#869] Link to stats docs from extension docs
[#538] Created package install instructions

* Deleted virtualbox specific instructions (outdated).
* Deleted ec2 instructions (outdated).
[#839] Minor edits to stats extension docs

- Edit the opening sentence, it's the stats extension that analyzes the db
  not CKAN (this is picky)
- Also mention that there are tables and graphs!
- Remove weird capitalization in bullet list
- Put built-in page view tracking before ckanext-googleanalytics and tweak
  the link to read a little better
- Add an example of ckan.plugins = stats, also cross-ref to the ckan.plugins
  docs
- Add link to stats page on demo
Merge branch '839-stats-doc'
[#886] Remove  from tracking.js because it breaks IE
Merge pull request #886 from okfn/886-js-console-log

IE bug with tracking.js
Docs: add note about where an org's first admin comes from
[#888] Change path for cache dir and simplify options

The data, sessions and sstore dirs were created in /etc/ckan/default.
This creates permission problems and is not the natural place to store
this kind of files. The main cache dir is now /tmp/s(ckan.site_id)s
(generally /tmp/default). The beaker dirs will be created there if not
defined in the config file. This will ease the packaging and simplify
the installation. Also our cron jobs for cleaning files look for them in
/tmp.
Merge pull request #888 from okfn/888-cache_dir-path-deployment.ini_tmpl

Fix cache_dir and beaker paths on deployment.ini_tmpl
[#538] Various tweaks on the package install docs

They include all the comments made on the pull request discussion.