Adress most of the second round of Angelaccio's review comments

This commit applies most suggestions which were made on the MR.
Most notably the DolphinUrlNavigator class is split up which leads to
the creation of a DolphinUrlNavigatorsController class.

Additionally some minor coding style and const correctness changes are
included.

The error value of cached integers is changed from -1 to INT_MIN
because situations could come up in which -1 would be a valid value.