sov-modules: Add `transactions` to the module system.

[bkolad]

If a module method returns early, we need to revert all state-related changes, for example:

fn foo(&mut self) -> Result {
   ...
   self.some_value.set(x);
   let v = self.some_other_value.get()?;  <- returns because of an error 
   ...
}

Shouldn't persist x or any other state change.

[preston-evans98]

@bkolad, Should this be part of the Alpha release? Adding for now, feel free to remove.

[bkolad]

This is already implemented (we revert in AppTemplate in this case), I forgot to close the issue.