This was supposed to be split into multiple commits to make it easier to understand
but I failed to do it properly. So this is the list of changes:
- New analytics_indicator_calc db table to store indicators calculations
- Reuse previous calculations during prediction/training; other models
previous calculations should also be reused as long as they belong to
the same sample (sampleid depends on sampleorigin), time range and indicator
- Allow bulk inserting of these calculations as this can hurt database performance
- Block the same analysable to be analysed for training and for prediction
- Use a new instance of the target and use it for is_valid_* functions
as using ::is_valid_sample can lead to problems if people
uses it to cache stuff
