WebBrowser objects aren't destroyed on close tab

[Walkman100]

Original issue: Walkman100#4

WebBrowser objects aren't destroyed when a tab is closed, only the tab is destroyed:

BasicBrowserGecko/BasicBrowser.vb

Line 69 in 4e55fc5

TabControl.TabPages.RemoveAt(TabControl.SelectedIndex)

[Walkman100]

This is mostly fixed with 0931d67#diff-30d64336f8d58272a3d40aeb8ca8d932R68, although that just tells the WebBrowser to navigate to about:blank before closing the tab. I couldn't find a method to destroy the WebBrowser completely.