[WIP] Added ability to list file sizes and limit output by flavor.

This adds some new options to the bundle:list command:
* New ```--size``` argument outputs file sizes for each file (in bytes) along with the total size of the bundle.
* New ```--human_size``` argument outputs human readable file sizes for each file along with the total size of the bundle.
* New ```--flavor``` argument allows you to specify a flavor and limit output to files only belonging to that flavor.

**TODO:**
* Improve new ```size_for_file``` method. The code is quite messy and I need to determine what to do if there are both compressed and uncompressed versions of a file.
* Update tests.