Remove ol.source.SourceOptions typedef

The ol.source.SourceOptions type is already declared in objectliteral.exports, so it should not be declared in the ol/source/source.js file.
Source option "projection" is a ProjectionLike
Make the generated Export classes accept undefined

We have constructors, like ol.View2D and ol.control.Attribution, whose "options" argument is optional (opt_options). But currently, we cannot do "new ol.View2D()" in uncompiled code that uses an ol3 build compiled in advanced mode. This commit fixes that by changing the generated Export constructors.
Merge pull request #384 from elemoine/optional

Exports fixes