Implement splitting types per file per namespace

[gvlasov]

Problem: When you have to use ModuleWriter (e.g. to get usable enums instead of only type definitions), you can't have types with the same base name but from different PHP namespaces.

Solution: Group code per namespace and output it in a corresponding directory structure, where the last part of the namespace is used to name the output .ts file for the namespace.

Example output structure:

src/app/resources/ts/dto/App/Data/Products.ts
src/app/resources/ts/dto/App/Data/Products/Attributes.ts
src/app/resources/ts/dto/App/Data/Users.ts

Introduces new config option:

    'split_modules_base_dir' => resource_path('ts/dto/'),

If it is set, TypeScriptTransformer ignores output_file config option and uses an alternative strategy for bundling the code that puts types from every namespace into their own file, with directory structure mimicking the namespace parts.

Otherwise puts all code into output_file as usual.

Notes

• Works well with Introduce Compactor to shorten output namespaces and type names #104 producing very simple output directory structure.
• This implementation is good enough for my use case, but if you give me specific missing test cases and other changes/redesign that need to be implemented for this to be mergeable, I'm open to finishing it according to your standards.

[gvlasov]

Had to integrate #104 here because locating module paths requires logic from there in order to work with compacted namespaces, these two are a single PR now.