This shows the following actions:
* Reload Tab
* Duplicate Tab
* Move Tab
* Move to Start
* Move to End
* Close Tab
* Close Other Tabs
* Close Tabs to Left
* Close Tabs to Right
* Close Other Tabs
By default, Qt will grow the width of a tab button to fit the title text
of the tab. For long titles or file:// URLs, this looks rather bad. This
sets a min/max tab width to prevent such infinite growth.
To do this, we have to subclass both QTabWidget and QTabBar, because the
functions to be called/overridden are protected.