Added checks in BB code tests on whether previous test left us on topic creation page.

Since it's possible that the test fails and leaves us on the topic creation page and then
next test tries to open main page, we can get into a situation when browser asks us
whether we really want to leave the page (prev test entered some data). This means
that all the tests fail afterwards since they can't make the browser leave the topic
creation page. So current fix checks on the test start whether