Fix account currencies and hedged CSV imports

[ChristopherDownie]

• Add saved offline exchange rates and use account currencies across the dashboard and calendar. Fixes Dashboard ignores account currency and sums mixed-currency P&L; proposal for base-currency FX conversion #31.
• Import Open/Close Long/Short CSV actions without mixing hedged positions. Fixes No work with Futures into CSV #22.
• Organize Settings into sections and improve account creation and navigation.