Fix accuracy circle color not being set correctly

[cammace]

Closes #482

[LukasPaczos]

Android color ints are not supported in Expressions so we need to convert them to RGBA strings. Try

locationFeature.addStringProperty(PROPERTY_ACCURACY_COLOR, PropertyFactory.colorToRgbaString(accuracyColor));

instead of pushing the Android int @cammace.

[cammace]

That did the trick, thanks @LukasPaczos. I made a note to add information about that method in our docs.