Shield images exceed maximum OpenGL texture size on older devices

[matteblair]

Currently bubble-wrap-shields-international@2x.png is 1014 x 3696 pixels and bubble-wrap-shields-usa@2x.png is 1792 x 3578 pixels. For an older generation of devices including the iPhone 4, Galaxy Nexus, and Raspberry Pi, this exceeds the GL_MAX_TEXTURE_SIZE limit of 2048 pixels (in either dimension). This means that these devices will fail to display any sprites in either of these images.

We can continue to support this generation of devices if we organize our sprites into pages of at most 2048 x 2048 pixels. I think it's worth a try!