Added 4 new events, Improved difficulty options, Better rare earth metals model

[1.35]

1. Difficulty slider now influences how frequently assassination attempts can be made.
2. Fixed bug where the polls screen could not be loaded correctly by the 'go back' buttons.
3. Changed the debt crisis icon so its more understandable.
4. Difficulty slider now influences chances of a successful assassination attempt.
5. Difficulty slider now influences the true success chance of a media spin event.
6. Difficulty slider now influences the final chance of a minister resigning.
7. South Korea now reverses surname and forename when both are shown.
8. Changed 'none' to 'minimum' for many sliders so they are less confusing.
9. Fixed a bug where new policies implemented due to donor demands didn't affect cynicism or show up on timeline.
10. Reduced the political capital cost of the speed cameras policy.
11. You now cannot cancel any policy the same turn you implemented it, even if it was a donor or coalition demand.
12. Introduced new 'Rare Earth Prices' simulation value, and changed icons for Rare Earth Mining & Crisis so the imagery is consistent.
13. Adjusted icon sizing algorithm so it ignores the influences upon situations that remain untriggered, to declutter main UI slightly.
14. A whole bunch of graphs now have percentages shown in tooltips over each point.
15. A button now pops up on the top left of election results screen after the result to allow you to save a screenshot with one click.
16. Added Falkland Islands and Russian Ships as new UK-only events.
17. Added new heatwave and black lives matter events.