Unified Icon component for web and native

[tsareg]

Now we have generic Icon component which loads Jitsi-specific Ico Moon font icons or Font Awesome font icons.

Also replaced Font-Awesome sources with NPM module.

[tsareg]

@yanas, as for our discussion about how to use icons from Jitsi fonts.
Actually, we can use not SVGs, but a font icons with classes. But this will require loading eot/svg/ttf/woff files. Do you think this is a better solution?

[yanas]

@tsareg I read some articles comparing svg and fonts, which I haven't spotted before and I actually don't mind the svg solution. It has it's advantages! We just need to make sure that it has good browser support (from what I read it should be ok, but still I spotted some comments about IE9). Also I read somewhere that some problems were experienced on Android. So let's make sure we check those if we haven't already.

[tsareg]

@yanas I've changed code to use font icons instead of svg.
As for Android issue, I expect it's something with react-native-vector-icons lib setup and it's not a part of this PR.