Added an importer for TypeScript definition files (.d.ts).

This importer can read a .d.ts file from TypeScript and
translate it into a .scala files that defines the same
classes, interfaces and ambiant variables and functions
as the TypeScript definition file.

Being a source-to-source translation that does not build
an actual symbol table, the output might need to be
reviewed by hand afterwards. But it should output a
pretty good guess automatically.