initialized reqtime with -10min
improved AVM::Fritz::Box module a bit

* introduced new variable for initial reqtime value
* adjusted EXPORT_OK (added global variables)
improved content delivery of FakeAgent module

* introduced URL dependent data assignment
* adjusted test of AVM::Fritz::Box module
updated perldoc
added AVM::Fritz::Box::Session module

* added features for logging in and out
* added subroutines for checking of session expiration
* added some appropriate tests
* adjusted README and improved AVM::Fritz::Box' POD