The converter should modify the split_roman_empire_decision

[IhateTrains]

Currently it can be taken even if e_roman_empire only holds parts of Italy, and it automatically annexes the whole e_byzantium de jure (which exists when converting with the static de jure option selected).

Needed changes:

• Add the condition that c_byzantion must be owned.
• Modify the effects so it doesn't annex any foreign land.