Hide widget level filters when dashboard filters are active

[s1moe2]

Issue Summary

When dashboard level filters are enabled, all widgets still keep their individual filters, which produces a lot of visual noise and redundancy (I also found this mentioned on discuss).
There may be use cases when both dashboard and widget level filters are needed but generally I see this as a "switch".

Technical details:

I've tried locally and came up with a simple solution to hide the widget filters according to the flag affected by the setting by basically adding this ng-if in [client/app/visualizations/index.js] (and a couple more lines, ofc):
template: `<filters ng-if="!dashboardFiltersEnabled" filters="filters"></filters>\n${Visualization.renderVisualizationsTemplate}`,
If I get some positive feedback on this and this behaviour makes sense, I'll create the PR.

But... As I mentioned (and I'm looking for feedback here), there may be situations when both dashboard and widget level filters are needed. For this case I suggest adding an extra setting along with "Use Dashboard Level Filters", such as "Show Widget Level Filters", for example.