Refactor Network Controller and Tile Loader Classes

[cecilianor]

The network handling classes need some cleanup. Things to inspect and possibly refactor:

Network Controller:

• [x] Rename the header and cpp files to follow C++ standards.
• [x] Check if the Tile Loader can set up its own Network controller (as a private variable), instead of taking it as a parameter.
• [x] Change the std::optional<QByteArray> NetworkController::sendRequest(QString url)signature and implementation so that errors are handled appropriately.

Tile Loader:

• [x] Check that all critical tile loader functionality returns a pair of std::pair<Data, ResultType>. Functionality is considered 'critical' if the program exits, crashes or otherwise fails if the result of that function makes it so that the map can't be loaded to the software.
• [x] Consider making the <Data, ResultType> pair into its own custom data type to simplify function signatures.
• [x] Add comments into the functionality that writes errors to the debug terminal. These can be left as comments, but should be available in the source code for future use in case something fails on MapTiler's end. This should be done to clearly be able to indicate if errors happen before parsing or rendering happens.

downloadTile Lambda:

• [x] This function needed additional error handling if the HTTP handling functionality returns a <Data, ResultType>. Update the lambda with this signature to fix the problem: auto downloadTile = [&](TileCoord tile) -> VectorTile

[cecilianor]

I just found a potential error in std::optional<QByteArray> NetworkController::sendRequest(QString url). This function can't have that type of signature since it handles different types of errors with the same error code. I will update the functionality to return a pair or tuple with data and errors.

[cecilianor]

I have set up the network controller as a private variable, and everything seems to work as intended. I'm going to make some general unit tests for the overall functionality. If everything passes, I will make a merge request on Monday.