Add support for ALDA 2 in the decompiler and importer

[truj]

There are some slight syntax differences between ALDA 1 and 2.
The decompiler was made before ALDA 2 came out.
Also the CLI might be different.

• Check if the decompiler still works with ALDA 2 (I'm pretty sure that's not the case)
• Add ALDA 2 support in the decompiler
• Add ALDA 2 support in the importer (probably necessary as well)

Maybe it's easy enough to support both versions. But if that's too much overhead, it should be ok to skip ALDA 1 support at all. I guess most people won't use it any more.

[truj]

Key signatures need to be converted in the decompiler. Everything else still works.

The importer can check the alda version and then decide what to do.

In the exporter this is not so reasonable because the target could be another system.
Of cause I could add a checkbox to choose the target version but I think that's not worth it.
So my decision is to stop supporting decompilation to alda 1.

[truj]

Upgrade finally done.

As ALDA 2 doesn't crash on too many MIDI channels any more, I was able to improve the Unit tests to import/export/re-import from/to several formats.
This revealed some bugs in other parts that I didn't find so far, and that are also fixed within this issue.

Two things are a little annoying:

• The unit tests where ALDA is involved for import take a really long time.
• From time to time ALDA crashes unpredictably, causing an EOFException in my tests.

A little more background information for those who are interested

I improved the MidicaPL language a lot in #79, now supporting bar lines and more compact syntax, taking inspiration from ALDA.
Then I wanted to support all these improvements in the exporter as well. That's what I did in #80, improving the decompiler a lot by the way.
I applied these changes also in the ALDA exporter (still in #80).

Here the improvements from #80:

• Added line breaks after a (configurable) number of elements (to avoid extremely long lines)
• Added bar lines whenever possible (assuming that each time signature event happens at the beginning of a bar)
• Fixed some bugs
• Added comments about source and target tick ranges to each line (can be switched off)

That was a lot of work. Compared to that, the upgrade to supporting ALDA 2 was trivial.
In the exporter I only had to change the key signatures.