On a new (Linux?) installation, if no sound output is enabled, opening "Preferences" crashes.

In mscore/preferences.cpp, seq is accessed but set to 0.

Added some safeguard checks.
Merge pull request #341 from mgavioli/qt5-preferences_crash_new_installation

QT5 - On a new installation, "Preferences" crashes
fix travis build
find lrelease and lupdate correctly
Set the tightbbox for unparsed chords.

... to ensure that they get spaced correctly.
Fix Staff &lt;barLineSpan&gt; file tag:

With the 'new' XML reader, tag attributes have to be read before reading the tag main value.

For Staff &lt;barLineSpan&gt; tag, this has not been adjust yet.
fixing 2 mistakes in instruments.xml

and instr_language.xml
add svg icon engine
fix #20970 : Glissando collides with elements before note
gray out inactive icons
colorize toggled icons
try something new for breaks design
fix crash in text indent more, ordered list
add simple system bracket
missing icon in Style->Text
tune icon color
make breaks and spacer bigger
fix overlap of lines in break symbols
pressed buttons have white icons now
update note duration icons