Error when calling build_model

[ff6347]

@hsonne I having some trouble with spot 41 of user 9 creating a model.
The error I get is:

{"data":{},"success":[false],"message":["Error : Constant variable(s) found: log_e.coli\n"]}

I'm running on ffhpredict@v0.9.1

re #41 #48

Doing releases right before ❌ MAS 🎅 Ho ho ho

[hsonne]

@fabianmoronzirfas I checked this error. It means that the E. coli concentration is (by coincidence) the same for all days on which measurements of all uploaded types (hygiene, rain, flow, irradiation, ...) are available. It is a plausible error. @wseis Maybe we could catch this type of error and give a more clear error message.

[ff6347]

I think we should create something like an error database. So we can assign meaningful messages to errors that pop up