Tweaks for DEGIRO

Unofficial extension; not affiliated with DEGIRO in any way. This extension implements minor but impactful UI enhancements for the DEGIRO trader interface (trader.degiro.nl). It requires no permissions (other than running on the trader's domain) and does not collect your data in any way. Everything is computed locally from numbers already visible on the page. Current features include (to be expanded in the future): - Sticky headers for the several tables, so they remain visible when you scroll down - A Break-even column for the Options table, based on the strike price and midpoint of the Bid/Ask price - A Spread column on the product search page that calculates the difference between the Bid/Ask as a percentage of the midpoint