MDL-59067 analytics: Store indicator calculations

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

analytics/classes/model.php

@@ -293,6 +293,12 @@ class model {
             throw new \moodle_exception('errornotimesplittings', 'analytics');
         }
 
+        if (!empty($options['evaluation'])) {
+            foreach ($timesplittings as $timesplitting) {
+                $timesplitting->set_evaluating(true);
+            }
+        }
+
         $classname = $target->get_analyser_class();
         if (!class_exists($classname)) {
             throw new \coding_exception($classname . ' class does not exists');