DevTest: Formspec tests, children getter, better lighttool

[Wuzzy2]

It's a minor improvement for DevTest:

• Adds more formspec tests for sound styles and model[]
• Adds a "children getter" tool. This shows the list of objects attached to another object (using get_children)
• Improvement of the light tool: With the "place" key, you check the light level of the node that you touched. Also displays the pos of the node you just checked. Tooltip was also improved.

To test the children getter, just attach objects to each other, then use the children getter on them.

[Wuzzy2]

I've added the "Node Meta Editor" to DevTest, this is a tool to edit and view node metadata.

[Wuzzy2]

How about removing metadata fields?

This is done by clearing the value field and then hitting "Set value".

[Wuzzy2]

All requested updates done!

[SmallJoker]

Works (quick test)