Fix metronome alignment.

Fix metronome alignment.

Don't align on KeySignature unless explicitly requested via
'break-align-symbols and make order of 'break-align-symbols
significant.

* remove `key-signature' from 'break-align-symbols

* acknowledge break_alignment, and set this as X-parent
  instead of break_aligned, but only if found break_aligned
  is visible

* add regression test to test ordering

* tweak existing test to reflect change in default for
  'break-align-symbols