Refactor game identifier, steam client and steam app data model

[lukatarman]

Description

• Refactor the game identifier, the steam client and steam app data model. The files have a lot of repeating code that can be refactored and made much easier to read & understand.

Technical Design

• in the steam app data mode, change the specific triedVia methods into one triedViaSource(source){} method
• same with the new failedVia method
• in the steam client, do similar with the html page request methods
• rename tryViaSteamWeb, etc to checkIfGameViaSteamWeb, etc
• in the game identifier refactor as you see fit. It will become clearer when everything else is refactored. TBD.

Only start this issue after #199 and #200 are finished