icons: Add Koala's SVG icons

This will be the source for the bitmap icons we will need in various
sizes.

This is a part of issue #3
icons: Add 16x16 renderings of Koala's icons

This is necessary for the input method switchers in various desktop
environments.
icons: Use the 16x16 icons for the input method switchers

This is a part of issue #3
Merge pull request #22 from Cangjians/icons

Add Koala's icons