[#12016] Added method into every service as a prototype for fetching specific data

• Added first prototype versions of service methods that will fetch specific data
• Added some basic comments and TODOs to problems I already faced or problems we will need to resolve with Mr. Pícha (e.g. not existing properties or optional properties)

This is just a prototype and this should serve (mainly) to managers @vandl & @JakubHomolka so they can see future structure and how the data is downloaded using the maven library