Error if user has already been invited

closes #3681
Merge pull request #3708 from felixrieseberg/iss3681-2

Error if user has already been invited
Updating Casper to latest
Version bump to 0.5.0-rc3
Fix 'broken' debug tools template

closes #3715
- Includes wrapper class for @pauladamdavis css
Merge pull request #3717 from felixrieseberg/iss3715

Fix 'broken' debug tools template
Fix rss content's url to the RSS feed

fixes #3719

- correctly sets the path to the RSS feed for tags and authors
Fix wrong author slug on user settings page
MU Importer - Assign objects correctly

fixes #3716

- change the importer to not override any user details
- only set published_by if it is not already set
- import users before anything else
- process the import and map user ids to existing users
- test fix - owner should have owner role
- test fix - catch invalid success in importer
Merge pull request #3726 from ErisDS/issue-3716

Fixed MU Importer
Merge pull request #3723 from JohnONolan/wrong-slug

Fix wrong author slug on user settings page
Ensure PSM author is reset when changing posts.
Merge pull request #3722 from hswolff/rss-atom-url

Fix rss content's url to the RSS feed
Merge pull request #3729 from rwjblue/ensure-author-in-psm-is-reset

Ensure PSM author is reset when changing posts.
Update authentication endpoint for subdirectory

Fixes bug where user is unable to log into admin when subdirectory is specified
Expose blog URL to client app

 fixes #3724

 - provide config.url to the ember client app via a data attribute
 - create server and client side helpers to output the URL
 - wire up the client side helper
 - add a class for testing, and add tests for both the server and client side
Merge pull request #3730 from jyek/auth-route

Update authentication endpoint for subdirectory
Adding author pages to cache invalidation
Merge pull request #3731 from ErisDS/issue-3724

Expose blog URL to client app
Merge pull request #3735 from ErisDS/cache-invalidation

Adding author pages to cache invalidation