macosx: create also standalone application bundle, wip

working application, but missing icons in menu entries and buttons
macosx: print info about the steps performed after calling py2app
macosx: manual steps required to finalize standalone .app

- prepare .app bundle for manual steps
- print instructions for manual steps
macosx: background for DMG disk image
macosx: JSON file for DMG building with appdmg

appdmg is a node.js package available through npm
macosx: script to build fully standalone .app and DMG
macosx: add DMG creation switch to build-dmg.sh (useful for debug)
macosx: include libportmidi.dylib in standalone .app
macosx: make Frescobaldi.app pick up the included libportmidi.dylib
macosx: more general patch handling
macosx: make Frescobaldi.app use the bundled Python for scripts

Fixes the problems with LilyPond's scripts, namely convert-ly and
musicxml2ly.

The Python interpreter currently bundled in LilyPond.app is almost
unusable and I had troubles trying to use the system-provided
interpreter (/usr/bin/python).
macosx: update list of expected /usr/bin/strip warnings in build-dmg.sh
include Mac OS X build files in source distribution
update Mac information in INSTALL
macosx: command line argument for path of PortMIDI in mac-app.py
macosx: variable to change MacPorts location in build-dmg.sh
macosx: no need to install node.js thorugh MacPorts in build-dmg.sh
macosx: build-dmg.sh adds architecture to DMG name
Merge pull request #446 from dliessi/standalone-mac-app

Standalone Mac application bundle