Templates Updates

Hi, 
I made changes only on templates, didn't replace current skins :

- Updated Nexus 5 template with new picture
- Added Nexus 6 template
- Added Legacy HTC G2 template
- Refactor

I actually didn't change the current skins because I don't use them, as I use skins to record demos, I need more speed so I scale down the Nexus5 xxhdpi −> xhdpi and I also need a 4:3 emulator window, this is why I need to be able to export skins easily. Feel free to give your feedback on new Nexus5 skin before merging, also let me know if you want me to export a skin, or if you encounter difficulties exporting them yourself, or if you want to improve something...

Thanks for maintaining this project !
Cheers, 
Nicolas.