Make py2app includes consistent with py2exe

and make indents standard.
Remove obsolete ref to cgi
Eliminate unnecessary modules
Revert "Remove obsolete ref to cgi"

This reverts commit 95ec346c2ada3394fdb8db452d824ba047e1ac7a.
Add back use of cgi escape

Added originally in 27cc6d7086576ae7fce22d47ead7f863a937f524 and
reverted in error in 5a2eee348484403bf10d0617ce4dff462db1ad2f.
Remove cgi from exclude_module list
Restructure to import in correct order etc.
Merge pull request #316 from Sophist-UK/sophist_exclude_unneeded_dist_files

Exclude unnecessary python modules...
_fill_try_list(): do not enter loops if not needed
Reduce code redundancy using intermediate variables has_front and has_back
Introduce class CoverArt
Re-order _fill_try_list arguments, place coverartobj in first position
Re-order _walk_try_list() argument, place coverartobj in first position
Re-order _caa_json_downloaded() arguments, place coverartobj first
Re-order _coverart_downloaded() arguments, place coverartobj first
Move most code from coverart() to new coverart_init()
Move class CoverArt and coverart() at end of the file
Convert most functions to class methods
Move coverart_init() code to __init__()
Convert album argument to class property