when switch to "raw Document" metric type we do free all "Group by"
however when we switch back to another type we do not reset the default aggregation (date histogram)
Thus all modification will through exception as no "Group by" is defined and panel should be recreated
the fix will reintialize the "Group by" by setting default value

 when selecting Raw Documet metric type, the $scope.target.metrics was replaced by [$scope.agg],
 however the pointer to this variables is shared with metricAggs.
 Instead we free the array and add $scope.agg

 it allows to specify the result set size in raw_document.
 Example: table  panel could show more (or less) than 500 line if needed.
 Added test to spec

chrome: an attempt to fix scroll issue with chrome, but this did not fix the problem as it seems to be caused by some interaction between graph rendering and scrolling, #8494

* remove X-Forwarded-* headers added by nginx when proxying data source & plugin requests

* properly handle X-Forwarded-For

fixes #8446. Data with all values equal to zero, creates a max with the
value of Infinite. The for loop for creating ticks then gets stuck in an
infinite loop. This fix resets min and max and creates some fake ticks
for the y-axis if the min and max are not finite numbers.

Resolves issue #8467

fixes #8446. Data with all values equal to zero, creates a max with the
value of Infinite. The for loop for creating ticks then gets stuck in an
infinite loop. This fix resets min and max and creates some fake ticks
for the y-axis if the min and max are not finite numbers.

- Move export csv options to modal dialog

Adds series override options for dash spaces and dash length.

Resolves issue #8467