Merge pull request #252 from PeterBjuhr/export-musicxml

Basic musicXML export
highlight-timing: Make highlight matches infinite

Initial idea: Don't stop the highlighting of matching brackets after
one second.
This will of course have to be made configurable later.
highlight-timing: load highlight time from settings

Loads the value for the highlight time from the settings.
Currently there isn't a user interface for this so this means it will
always be 0 (= infinite)
dont use split() but os.path.splitext()
highlight-timing: create Preferences page (init)

Create a new page for the Preferences dialog "Editor Options".
This is for now simply a copy of the "Helpers" page.
just write musicxml output to file

todo: use the write() method of the elementtree document, this also
handles encoding correctly (now it is encoded twice in some cases possibly)
neater to just use XML files and not other types
highlight-timing: Make Preference page work (init)

Now the Preferences page works for highlighting of matching brackets,
the value set here is respected in the matcher.
highlight-timing: Only load settings when changed

The value for the highlighting duration is now read from QSettings
only on app.settingsChanged (instead of on each match)
highlight-timing: Use theme icon

I'm not sure if that's a good one, though
Merge pull request #253 from uliska/highlight-timing

Make match timer configurable
changed to xml.etree