added new methods to client interface
added new interface for new data access
added new class for the new data access
changed interfaces to accept and return multiple files
added api base url to constructor
added method for generating the query string of filenames and checksums
added task completion source as a field and added method for handling download completed logic
method generates query string, calls api, transforms data
added nullchecks and error handling
Merge pull request #24 from IrradiatedGames/implement-method-for-find-plugin-by-file-name-and-checksum

Implement method for find plugin by file name and checksum