convert as many "enum" as possible to "enum class", and make them ": char" in the due course #7

Follow up of PR #914, #927, #935, #936, #946 and #1005
Several enum types are "enum class" (i.e. typesafe C++ enums), several others are not.
Also making them ": char" should reduce the size of structures using them.

The big changes, mainly in libmscore, are hopefully done, over to the smaller ones in mscore.