Add target for T2Runtime

[Former user]

Wouldn't it be nice to have a make target for the runtime data which would install the data in $(DESTDIR)/share/tempo2, and point to this by default?

[Michael Keith]

I have considered this in the past, but there are a few potential issues that need thinking about:

1) Would probably want the tempo2 to look into this directory by default, i.e. not check $TEMPO2, in a similar way to the new plugin system. 2) Need to check what happens with parallel installs. 3) Is there a danger of people accidentally clobbering clock files.

I can think about it again, but really this is a feature request.