Add a "last resort" string-to-date conversion routine

Problematic feed reported at http://forums.cocoaforge.com/viewtopic.php?t=26323&p=137277
Improved UnifiedDisplayView

- finer detection of cell size problem (don't do anything special if the size should remain unchanged)
- simpler method for resizing a cell (set frame size to a small one and ask for a content redraw)
- make sure we position correctly the webview inside cell
Add fix for some iframe videos not showing
Merge pull request #217 from barijaona/bugfixes

3 really important bug fixes