HNotate, Bala and TabApp

Copperbox revision 372.

Some rework on TabApp and minor changes to Bala and HNotate.

I thought I'd look at getting TabApp to work, as it will be something to stretch HNotate with. It has already show a limitation in HNotate - individual notes within chords should have annotations so they can have string-numbers (the same goes for tuplets).

I've split TabApp into two parts, one LpTab is a simple tab to LilyPond converter, the other is new code but still called TabApp. There is a rationale for having two versions. LpTab has a very strict parser, it will abort on a parse error. Guitar tab files only have a loose specification as they're intended for human reading - with LpTab I'm trying to find out a good subset that corresponds to LilyPond's tab capabilities. For TabApp I want the parser to be a bit looser, it should be able to at least run on tabs from the wild whether or not it can turn them into good output.