[FEATURE] Allow provider extensions to be registered using PHP

This feature requires a PageController to be present in the provider extension. If so, the provider's collection can be enabled from ext_tables.php by inserting:

```
Tx_Fluidpages_Core::registerProviderExtensionKey($extensionKeyLowercaseUnderscored);
```

Fluid Pages will then look for template paths in `plugin.tx_thatext.view` - which is already fully compatible with standard Controller paths. In other words, to make any Extbase extension a provider of page templates, simply add a PageController which subclasses Fluid Pages' AbstractPageController and add the registration in ext_tables.php - and you're done, ready to use your PageController exactly like you would use any other Extbase controller with one added convention: one page template selection equals one controller action. Templates are still detected based on files in the path but now, each template in addition requires a corresponding Controller action.
[BUGFIX] Add missing consideration of native View paths

This fixes an issue with an invalid resulting array when retrieving global (indexed by extension key) page template configurations. After this, native paths for extensions registered through PHP also get considered by the code in question.
Merge pull request #23 from NamelessCoder/controllers

[FEATURE] Allow provider extensions to be registered using PHP