Add the email to the flash messages in Registration.handleStartSignUp

This is done so that the email address that the user shall check can
be displayed in the target page / template.
Add support for plain text, only html and multipart emails.

The templates plugin already allows to return customized content
for the emails. Though, the email content is already sent as content
type html.
This improves it to allow sending only text, only html or multipart
emails. The templates plugin now returns a tuple of Option[Txt] and
Option[Html], so that clients can choose which parts they want to
provide. As the mailer plugin handles null or empty content gracefully
we can reduce None simply to null or an empty string (the latter is chosen
because the mailer plugin also passes an empty string if a part shall
be omitted).
Update documentation for TemplatesPlugin text/html/multipart support.
- Added a makeTransient property for the authenticator cookie.
- Fixed: absolute timeout was not being picked up from the conf file
- clean securesocial values after login from the session
- renamed keys used in session
updated change log
update version in docs
updated docs
Merge pull request #162 from magro/plain-text-html-and-multipart-emails

Add support for plain text, html and multipart emails in TemplatesPlugin
Merge pull request #161 from magro/add-email-to-handleStartSignUp-flash

Add the email to the flash messages in Registration.handleStartSignUp
Allow overriding Registration step redirect targets.

Registration actions like handleStartSignUp etc. redirected to login,
which is not always desirable. To allow users to change this
several properties are introduced (that can be omitted):
* onHandleStartSignUpGoTo
* onHandleSignUpGoTo
* onHandleStartResetPasswordGoTo
* onHandleResetPasswordGoTo

In securesocial/defaults.conf these are set to "/login", but this
could also be left out (if a property is not set it's set to
login either).

The properties based approach is chosen because there are already
an onLoginGoTo and onLogoutGoTo properties.
Update documentation for configuration of registration redirect targets.
Change property names for registration redirect targets.
Merge pull request #160 from magro/overridable-registration-step-targets

Allow overriding Registration step redirect targets.
updated change log