Fix reloading functionality

[Baitinq]

Previoulsy, reloading went back to the first page loaded by WebView::load() or WebView::load_html(), as they are the only methods that modify m_url, which is what the reload loaded. Now we handle reloads in Tab.cpp by simply loading the last entry in the m_history.

[gunnarbeutner]

One more thing about the commit message: Previoulsy.