[BUGFIX] more fallbacks if ConfigurationManager::getCurrentPageUid cant ...

...find the current page id

I create a "Text with Picture" content and than i try to link this picture that does not work.
At the first time if the element browser pop up i see my custom tab.
But if i click the tab it disappears.
This is because the ConfigurationManager->getCurrentPageUid() can not resolve the current Page Id and
returned Zero because at this time there is no $_GET['P']['pid'] param in the URL.
But at Page Zero there is no PageTS...
I add some Fallbacks inspired by the BackendConfigurationManager from extbase

http://typo3.org/api/typo3cms/class_t_y_p_o3_1_1_c_m_s_1_1_extbase_1_1_configuration_1_1_backend_configuration_manager.html#a3bfe3452963b48e44edfe97354d74bb0