[Admin panel] add main case study selector

[AleksandraKozubal]

Admin should be able to choose which case study is presented on home page. To do:

• [ ] admin panel case study selector
• [ ] display it on the home page (now it's mocked)

There is a need to remember that this case study design has certain structure: Project : ... Client : ... Objective : ... Scope : ... Technologies : ... but when it comes to the details page of the case study, we will probably show it in a different, detailed way.

[AleksandraKozubal]

We decided that main page case study is going to be changed rarely, so the best option is to leave it as it is and do not create separate admin panel tile for it - just change in blade when needed