Improve XWikiLogin.

If you have a form authenticating against XWiki/XWikiLogin, you can
now define a xredirectFailedLogin parameter to redirect the user
in case he entered wrong credentials. This is useful for custom login
pages that want to show the errors by their own.

Improve readability by indention.
Fix parameter validation for registration.

Make the muting for errors of the location parameter in the
validation work.
Improve SocialLoginToolGroovy for auto registration of users.

A set of switches and parameters to enable the SocialLoginToolGroovy
to handle one click social sign ins, even for new users. Basically
you need to prepare the Tool in the session of the foreign page
and call $tool.setAutoCreateUser(true) to skip the registration form
for new users.
Added extra confirmation email for the autoregistration flow.

The newly added email contains the users password. So users which where
auto registered to Curriki do get the username and password sent.
Extract Curriki Analytics JavaScript to own file.

The Curriki Analytics functions "Curriki.logEvent" and "Curriki.logView"
are now in "curriki/curriki-analytics.js" which is concatenated to the
main curriki javascript files via concat_js.sh. We also build a separate
file with these functions ("webapp/js/curriki-analytics.js") so we can
use it without loading the whole Curriki JavaScript app.
Curriki MembershipDrive.

A working version of the MembershipDrive.
Working login via existent Curriki account, facebook or google is
possible. Make usage of the new auto create user capabillity to
register new users without their interaction.
Read xwiki/src/main/pages/MembershipDrive/readme.md for more
information.
MembershipDrive Readme.

Added a readme with some instructions and information
about the MembershipDrive.