file_packager: Add suport for glob or loading file list from file

Sometimes you might not want to pack all files from a specific folder, but only some. In this case glob pattern (there is a function in the Python standard library for doing this) would be useful like assets/**/*.png, but it is not supported by file_packager. There is a workaround - you can specify all files explicitly by hand or generate a command line using another script. But in this case you may hit command line length limit on Windows if you have too many files. In such case it would be useful to be able to read file list from text file (e.g. compilers allow you to pass options using text files). But such feature is also missing from file_packager.