81: Separate post-related functionality

[EugeneTurkin]

We want to change our project layout from "package by layer" to "package by layered feature". It's a good practice and will allow us to avoid having huge files with thousands lines of code. As a part of this we need to move all post-related functionality to a separate directory.

So in the scope of this task we need to move all post-related code to the separate package inside our src directory and check that everything works fine after these changes.

[birthdaysgift]

I don't know why this PR is closed. This functionality is merged to develop branch without any issues.