Make safeBrowserName usage optional

[folderol4]

All other karma reporters by default generate in names like 'Chrome 53.0.2785 (Mac OS X 10.11.6)'. For some reason this report replaces spaces with '_'. It would be nice if we could turn this off so everything shows up in the right browser directory.

For reference, this reporter is doing the following:
var safeBrowserName = browser.name.replace(/ /g, '_')

Either remove it all together, or provide a new grunt option, 'useSafeBrowserNameDir'