Use the FileService for TemporaryFiles, LibraryFiles and IssueFiles

[NateWr]

Describe the problem you would like to solve
The FileManager classes are still used for TemporaryFiles, LibraryFiles and IssueFiles. That means we have two sets of code for reading and writing files to the files_dir directory.

Describe the solution you'd like
Use the new FileService class to read and write TemporaryFiles, LibraryFiles and IssueFiles. That will allow us to remove the FileManager classes and better support remote files in other parts of the system.

Who is asking for this feature?
Developers