Fix the mess with the air mode

It turns out that we weren't automatically detecting the "air" mode. And so "air" trips were getting predicted as "car". At least sometimes, the prediction seems to have been made with high confidence, which means that it shows up as green. The user then confirms this using "confirm all", which just feeds into the prediction bias.

In this set of changes, we do the following:

* We identify incorrectly classified air trips through manual inspection.
* We build in a mechanism for manual correction - a script that works on a file with the corrections and sets the corrected_mode flag
* We add in support for the corrected_mode flag to correctly override the confirmed_mode flag if present, in:
  * the queries
  * machine learning pipeline

Finally, we change the machine learning pipeline to automatically predict the air mode as well.

BONUS FIX: Adda a README describing the various mode flags, and how they are used in queries and in the ground truth.