Changes to price calculations and more

Better handling of prices for transactions involving stablecoins.
Cryptocurrencies that we do not have market prices for are highlighted on the Transactions page.
The transactions edit page now shows if the value of the transaction was determined by our market rates or manually updated by you.
Additionally, manually created transactions will be marked as 'manual' on the transactions page.
Dashboard now shows stats for current year by default instead of last 1 year.