Dynamic translation and Post view configuration changes

[kantorii]

This request includes the following changes:

Prevent translated messages from being cached, so that language can be changed dynamically.
Added configuration for SECURITY_POST_FORGOT_VIEW
(This specifies the page to transition to after sending instructions to reset password.)
Added configuration for POST_SEND_CONFIRMATION_VIEW
Added many translations for Japanese.
Renamed translation file for nl_NL, because it is likely wrong.

Please let me know if you want to remove some changes. Of course, you are free to remove them yourself.

[kantorii]

Added another commit:

Don't flash message if there was an error sending welcome email.