Adds initial seven segment display component.

Adds Digital Dream and Dited fonts from fontsquirrel.com.
Fixes Crafty Text font bug.

The Crafty Text component had a bug that shared its font properties
with all instances of Text entities. Simple fix was to move the
property object initialization into the init() function instead of
letting it hang out at the component's top level.
First working scene.

Adds pushbuttons with locking covers.
Adds a Scene component to organize scenes into create + draw.
Adds an Offscreen component to start entities way off screen.
Refactors the main scene heavily.
Updates sprites + sprite sheet SVG.
Fixes lots of bugs.
Adds broken DotMatrix and RotarySwitch components.

Some code exists for DotMatrix, but it's wildly unfinshed.

RotarySwitch is completely empty.