Add images support

[acherkashin]

Reason

I see the following reasons to introduce images support in this addon:

1. In some cases, we need to use *.gif, *.jpeg, *.png instead of *.svg files
2. In some projects contain legacy with many *.gif, *.jpeg, *.png files

Changes

Image loader was implemented in the same way as svg loader.

How it looks

[Sqrrl]

Thanks. I've merged it "as is" for now (v2.4.0). I'm not sure, if it would be better to make it opt-in, though. The new tab could be undesired by some users.

[acherkashin]

@Sqrrl thank you!