param validation not caught

[DaveSkender]

When entering parameter values for the indicator detail Picker Form, unique parameter validations are not caught.
For example, when selecting MACD with erroneous Fast Period > Slow Period, it produces an error on the backend and a false selection record. These unique validations are not addressed, and may not be addressable, in the forms validation -- at least not easily, given all the possible permutations.

Recommend: on Submit do a trial GET and catch 400 errors before the detail Picker Form is closed and present instructions to user to correct. Do this before calling addSelection(). Or, refactor addSelection() to getSelection() subscriber model and then a new addSelection() just does the composition if getSelection() is successful.