Niklele/saveload

[niklele]

save and load to Documents, which is the recommended location. This should make it easier to get to the files for the share menu.

testGenerateExample:

• check that we can generate xml from music model
• check that we can load example from bundle
• check that the notes b/t them match
• check that the entire xml document b/t them matches

testSaveLoad:

• check that we can save xml to disk in Documents
• check that we can load the same file from disk
• check that the notes b/t them match
• check that the entire xml document b/t them matches

I modified the example file to support this and fixed some bugs in some of the xml elements like duration.