Properly escape cookie value used for autologin

The value of the cookie that is used for the "remeber login" functionality was not
properly escaped. This could be used to execute arbitrary sql when using a
recent version of mysql.
Do not regenerate the session id when logging in through a php session

Regenerating the session makes it impossible to use the backend in multiple tabs
at the same time.
Fix handling of integers in backend sql queries

In some places they were escaped but not quoted in the query. Now they are passed
through intval. This could be used to execute arbitrary sql when using a
recent version of mysql and if you have an account for the backend.
Prevent moving of/to sites the user does not have access to (backend)

We reuse code already in place that prevents access from editing these sites.
Hide unused input elements in the rights settings
Rework rights settings table to be clearer
Prevent uploaded scripts form being executed (in Apache)

Also add a section in README with recommendations for other webservers.
Remove unused backend modules that were visible in the rights dialog
Change licence from CCv3 to GPLv3
Bump version to 1.3