Add mobX to the project

[Ekaterina1994]

• [x] Change Theme by using mobX as a global store
• [x] Change Language by using mobX as a global store

[pp2amd6]

@tritonJS826 @Ekaterina1994 how QA Team should / can test that? :)

[Ekaterina1994]

Need to check updating theme, language and user logic

[EkaterinaSokolova-V]

`done