Expose all modules in application when no exposed-modules is set

[Kurren123]

Issue Notes:

• Had to change the Manifest type annotation to any in completeApplication as only any types were being passed in and there was no way of making exposed-modules nullable without breaking other stuff. Also, exposed-modules shouldn't be nullable anyway. We still return a Manifest however.
• Used the file paths to obtain the module names rather than having to read the source files and parse the elm to get the module name.

[Kurren123]

Just realised I didn't add documentation. Give me a minute

[Kurren123]

Done