fix(icon): mapping same icon does not warn

[liamdebeasi]

While working with Mike to test StarTrack, we discovered that mapping the same icon twice yields a warning when it should not.

Example

addIcons({ logoIonic });
addIcons({ logoIonic });

This can happen in an application where same icon is used in multiple places. In that case it's necessary to call addIcons since we don't know which place will be loaded first. In this case, no warning should be logged since these are the same icon references.