Significant slow downs resulting in data loss

[Slade1972]

Using either branch up to latest commit
Chrome: Version 41.0.2272.118 m (64-bit)

This seems to mostly affect larger story lists, however the issue manifested itself when <30 passages.
When adding a lot of passages (>5-10 passages) in a single session, and moving through the list of passages (to add story links), the software slows to the point that typing characters can take up to 20 seconds each to appear in the main Passage edit box.

When this happens, it is almost guaranteed that the last passage is unlikely to be saved.

To reproduce import a large story. Click through the list of about 7-10 passages and add a passage and link it up to somewhere (nonsense text will do), then click through a few more passages, add another, rinse and repeat. After a few times through this the software will virtually stop.