added commands state

[igorkorsukov]

Key points:

• Like with the register, there is a single interface for obtaining the state of any command; it uses the states of specific modules.
• The implementation of calculating the states of specific commands is located in the module that processes these commands.
• We need to manage all state changes ourselves to notify about state changes. (For simplicity, we can think of this as the availability of menu items, although in reality it's not directly related to menus.)
• I added constants for the commands there, and I'm still confused by this decision, since it will lead to one module being dependent on another... But in our case, they are already linked at the compiler level; the main thing is not to link them at the link level.

[igorkorsukov]

replaced by #90