Fixed .png

Changed .PNG for .png in some images
Merge pull request #1878 from al3mon/docs_tutorial_images

Fixed .png
Add missing messages block to base.html
Support activating accounts by admin users.

This patch supports activating users via the admin console. The workflow goes like this:

 * Administrator sets REGISTRATION_OPEN, ACCOUNT_APPROVE_REQUIRED to True and configures an email gateway.

 * Users try to register the site and are told the account is pending approval.

 * All users with the is_staff flag are emailed with a link to the Profile edit page.

 * As soon as any of the staff approves the user, he or she receives an email saying the account is active and a link to log in the site.

This depends on geonode-user-accounts 1.0.9 and has defaults in settings.py, local_settings.py and documentation production.txt about the new option.
More screenshots added in tutorial

Added more screenshots for admin and users in tutorial.

Fixed more .PNG images for .png
Merge pull request #1879 from al3mon/docs_tutorial_images

More screenshots added in tutorial
Merge pull request #1877 from ingenieroariel/registration-approval

Allow activating accounts by admin user
Updated changelog for version 2.4b6
Updated setup.py based on ppa versions
Corrected some of .txt documents

Corrected spaces, capitalizations, and some lines to improve the documents
Removed images with PNG in capital letters
Merge pull request #1882 from al3mon/old-images

Removed images with PNG in capital letters
Merge pull request #1881 from al3mon/docs_txt_modif

Corrected some  .txt documents
Added dependency on python-geolinks needed by latest pycsw
Merge branch 'master' of github.com:GeoNode/geonode
Updated changelog for version 2.4b7
Fixed short version of account requested
Renamed capital PNG to png in docs
add CSW bbox query test
Merge branch 'master' of https://github.com/GeoNode/geonode into thumbnail_simple