Add ability to turn off full depth array checking for large data sets

We need to be able to show large datasets with good performance, however the directive as it is written completely checks the config.series array on each $digest and the larger a dataset is the slower the directive will run. This change allows us to switch to $watchCollection checking which only goes 1 level deep so it will detect if we add a series or delete a series, but won't notice if we change individual data points. With this kind of checking turned on we get nearly the same performance out of large datasets that we do in a non-angular environment. I have written the change so that it will default to the old, full checking though.