Add target component feature

[petridw]

Addresses #2

Adds button that allows user to find a Vue component in debugger by hovering over components in the DOM. The debugger recurses through component tree to find the nearest parent component of the hovered element and expands that component into view, opening the debugger if it was closed.

Also adds a couple other small things:

• component props, data, and computed are now pulled out from the target component in debugger rather than in component-tree, makes it possible to initiate selections from debugger
• computed properties are now gathered by collecting keys from component.$options.computed
• component name is displayed in the overlayed component div when selecting a component

[dperrymorrow]

merged and published thanks!!