OCSADV-154 Update TOO target/guide to take real magnitudes

This is more fallout from removing the `brightness` string, which it turns out was used by the TOO servlet.

- Added `ImList<Magnitude> getMagnitudes()` as a member to `TooTarget`, and changed `TooUpdateServiceImpl` to propagate this information to the database.
- Added parser for magnitude lists like `1.2/UC/Jy,3.4/R/Vega`.
- Added code to `Http*` implementations of `TooTarget` to parse and retain a magnitude list.
- Refactored common `HttpTarget` superclass for `HttpTooTarget` and `HttpTooGuideTarget` just to get rid of some copy-paste. The refactored code looks kind of gross in the diff, sorry.
- Updated `README` to document the new request format. @swalker2m we need to notify the authorities of this change; not sure how to do this.