Add more game rules to choose from for milestone 4

[SamTheBlow]

Person reading this, if there are new rules you'd like to add, whether or not they're on this list, do it!

Here's an incomplete list I've written down for now:

Add money to the game

• [x] Add money as an int in Country
• [x] Save & load this new variable
• [x] Add new rule for how much money countries start with
• [x] Make the scenario give money to all countries at the start
• [x] Add a new chat command "/money" to see how much money you have
• [x] Provinces have a new int variable income_money
• [x] Save & load this new variable
• [x] Add new rule for how much income provinces give (random; constant; depending on pop size)
• [x] Make the scenario give income_money to provinces at the start
• [x] On new turn, give all countries money according to their province money incomes
• [x] On new turn, update the money income if it depends on pop size
• [x] Make chat commands show the new rules and information

Add the ability to buy a fortress

• [x] Add new rule for being able to buy fortresses
• [x] Add new rule for fortress price
• [x] Add a new chat command to buy a fortress
• [x] If no selected province, give system message
• [x] If selected province isn't yours, give system message
• [x] If not enough money, give system message
• [x] If already a fortress there, give system message
• [x] When it works, add a fortress to the selected province
• [x] When it works, reduce the country's money

Choose to have more population in starting province

• [x] Add new rule for more population in starting province
• [x] Make the scenario do it when the rule is turned on

Choose to start with a fortress

• [x] Add new rule for starting with a fortress already built
• [x] Make the scenario only do it when the rule is turned on

Add army recruitment to the game

• [x] Add new rule for enabling reinforcements on new turn
• [x] Add new rule for reinforcements size: random; constant; pop size
• [x] Add new rule for enabling manual recruitment
• [x] Add new rule for money cost per military unit
• [x] Add new rule for pop cost per military unit