pretty errors

[simonLeary42]

Our HTTP API constraints make it difficult to display alerts to the user without a fatal error. This commit needs to be reverted.

• header.php should check the current session for stored alerts and display them
• errorToUser() should should store an alert in the session rather than displaying HTML
• UnityConfig.site.enable_error_to_user should be removed
• badRequest() and internalServerError() should issue a redirect to clear POST data and display alerts, rather than dying
• forbidden() and redirect() should display HTML instead of calling errorToUser(), and still die
• UnityHTTPD::alert should be removed

[simonLeary42]

It would be nice if pages were also able to use something like UnityHTTPD::registerAlert any time before they include header.php, rather than using the generic "bad request" message.

[simonLeary42]

footer.php could check for errors as well and insert them into the HTML created by header.php, that would allow pages to use registerAlert even after including header.php

[simonLeary42]

$_SESSION['MODAL_ERRORS']: #350

[simonLeary42]

assertion on $_SESSION["MODAL_ERRORS"]: #352

[simonLeary42]

#160