Merge branch 'symbol_list_simple' into master

The following commits lead to uncompilable states before convert-ly is
being run, so they are combined into one merge commit for the sake of
bisection:

63a426b Run scripts/auxiliar/update-with-convert-ly.sh
5801d8b Change \footnote user interface and behavior to match \hide/\omit etc.
7dfbfb4 Let \overrideProperty accept nested properties
5ec4720 Change \tweak syntax to symbol syntax
a3d7090 convert-ly rule for \alterbroken, \accidentalStyle, \overrideProperty
15cae1f Change \accidentalStyle to get a symbol list as argument
53e6d49 Make \alterBroken, \hide, \omit, \overrideProperty, \shape take unquoted Context.Grob specs