Added support for console.log routine.

Support for the console.log routine has been added. 
Now the Console object is always inject into the JS engine.
The implementation of the Console class has been moved from 
the header to a .cpp file.
Now a call to `vg.headless.View.autopad` does nothing.

This change has been necessary because the `autopad` method 
relies on `bounds` routines.
`baseURL` is initialized according to the related command line option.

Now vegascene is able to parse the `-b` base option.
The `VegaScene::SetBaseURL` method checks if the passed option 
contains a protocol (file://, http://, ...) or is a local relative path.
Finally `vg.config.baseURL` is initialized.

`VegaScene::SpecFileContent` attribute has been removed since 
it is unused.

`vegascene` function now return an integer value:

- 0 if the whole processing went fine
- 1 otherwise.
Implemented a Data class for loading data resources from local files.
Merge branch 'master' of https://github.com/mcecchetti/vegascene

Conflicts:
	vegascene/main.cpp