Work in progress for chord symbol spacing.

This expands the containing segment to allow space for the chord symbol.
Further work required to allow a chord symbol to overlap segments that
do not have their own chord symbol.
Allow harmony to span multiple segments.

Also add a style setting for minimum chordname spacing.
Add stretch to notes under a long chord symbol.

Also, allow chord symbols to overlap if separated vertically.
Remove debug code and update some comments
Use a tight bounding box for Harmony layout.

Also normalise chord names to lower case when matching typed input.
gcc version check set to >= 4.7
Merge pull request #291 from heuchi/update_gcc_version_check

gcc version check set to >= 4.7
fix resource file for mac
Merge pull request #262 from softins/chord-symbol-layout

Chord symbol layout
synthesizer/midi cleanups
fix staff type of drumset
ignore .DS_Store files
add miditools
fix for midi export
fix compilation on MacOSX
fix #20695: add 2x resolution support for retina display text and score
fix follow text option in tempo text
improve Follow Text option for tempo text
do not create tempo text by default