Issue/230: Reworked styling of hint cards

[CodeWringer]

• This includes the hint cards included on the dynamic input dialog and actor health tab.
• Hint card styling is now clearly separated from the general-purpose forms styling, for ease of maintenance.
• The text of the migrator dialog was a tad small and has been set to the slightly larger default font size. This required increasing the height of the migrator dialog a little, so that the initial screen can still fit without scroll bars.