Fix handling of custom section titles

[kamilkrzyskow]

Fixes #73 To handle custom titles for sections the get_title function required access to the AwesomeNavigation.meta.sections structure to access meta properties of a given section item. One option was to pass the self reference as a parameter, but there was no such case in the code base. Therefore, I decided to transform the function into a class method to keep the current style. ✌️ I'm assuming no additional tests are needed.

[lukasgeiter]

Thanks for fixing this! The code looks good. That said, I would like to see a test that fails before the fix and passes after it.

[kamilkrzyskow]

Emotional damage... ok I shall see what I can do.

[kamilkrzyskow]

@lukasgeiter I think this should do the trick ✌️

[lukasgeiter]

Much appreciated, thanks Kamil!