fixed linechart zero-injection, closes #2102

[jthomassie]

@spenceralger this closes #2102
shelby and I worked on the update, we needed to distinguish between numbers and dates to fix sorting of values.
related to issue #1903 and pr #1968

[stormpython]

I'd move this var statement to line 20, right after

var flattenedData = flattenDataArray(obj);

[stormpython]

The reason issue #2102 occurred was due to the fix I put in for issue #1903.

The issue in #1903 was that the ordering of vertical bars was incorrect when using a terms aggregation with x axis values that are numbers. For example, when looking at the Count of Documents on a Terms aggregations with the Field of machine.ram or memory.

By default bars should be ordered descending with the x axis values with the highest y axis values appearing first. Since this is the default that elasticsearch returns, we only needed to order the x values by their indexed position in our zero injection code.

However, when x axis values are dates and a Date Histogram aggregation is used, we don't want to sort values by their index position since dates may appear out of order in some cases. So we needed to add code to check to see if the aggregation being used was a Date Histogram and to sort our values by the timestamps instead of by their indexed position.

[jthomassie]

@stormpython I fixed order of vars and updated comments with more details.
@spenceralger ready for review

[rashidkpc]

Is there a test for this?