Show "Saving... X%" alert on long-running save

[raineorshine]

Steps to Reproduce

1. Paste the contents of sample-1000-thoughts.txt.
2. After a few seconds, hit refresh.

Current Behavior

There is a confirmation dialog that warns the user that thoughts are not fully saved, but there is nothing showing them the progress.

Expected Behavior

After 5 seconds, if still saving, show an em alert that says "Saving... X%". The alert should update in real-time (throttled to 100ms).

Notes

Post the following information to this issue before beginning to implement a solution:

1. Identify where a long-running save can be detected.
2. Identify what the component parts of the percentage are, and how you will access them.