Fix SVG assets for Android

[fsih]

This is for the native library that we're building to help with https://github.com/LLK/scratch-android/issues/67. Android has its own SVG interpreter which has trouble reading some of our assets.

• Watermelon-a, b, and c need to have "svg:" removed from the SVG files
• Dinosaur1-c needs to have its path string for the body shortened (the longest path string). We can do this by bringing down the precision (we don't need so many numbers after the decimals. Probably like 2 is enough?)

[fsih]

One more:

• The basketball background fails to load and may sometimes crash the app. The fence in the background needs to be converted from a single shape with tons of holes to a bunch of criss-crossing lines. (While we are editing the svg, it would be nice to fix Fill tool fills the whole basketball background scratch-paint#273 also, by removing the rectangles drawn around the whole backdrop)

[fsih]

Adding critical since this is a Chromebook launch blocker