oll-doc: Fix header parsing

Fix header parsing when header does not end with a field
oll-doc: add (forgotten) 'status' header field

to be displayed in the metadata widget
lilypond-version-predicates: Add two test fields

Test fields to test the ability to use non-standard fields
oll-doc: Add non-standard fields to metadata view

non-standard fields are now displayed after the sorted
standard fields. Equally we have single line and multiline
edits available
Merge branch 'doc-script' into move-snippets