convert as many "enum" as possible to "enum class", and make them ": char" in the due course #4

Follow up of PR #914, #927, #935 and #936
 Several enum types are "enum class" (i.e. typesafe C++ enums), several others are not.
 Also making them ": char" should reduce the size of these structures.

Help in converting "enum AlignmentFlags", "enum ArticulationShowIn", "enum ElementFlag", "enum LayoutFlag", and "enum Repeat" into an "enum class" needed, these are used as flags (looking into these again right now).
 Also some help is needed to convert "enum TextStyleType" into an "enum class", but for different reasons (read: complexity).

Work in progress, don't merge right now, but comments welcome.