Initial support of GPX format
Deallocation of memory of a few pointers w.r.t. GPX files
Added isType methods for selection
Refactor of select method in score.cpp
Merge pull request #931 from jpirie/11769-gpx-support

Initial support of GPX format
Merge pull request #932 from BartlomiejLewandowski/selection-refactor

Selection refactor
convert enum UpDownMode into enum class
convert enum StaffGroup into enum class
convert unnamed enum into enum TextStyleType

more work needed to make it an enum class
convert enum BarLineType into enum class
convert unnamed enum into enum class IconType

and change to a better sentinel for end of list.
Also move the Q_DECLARE_METATYPE(Ms::ValueType) nearer to its
definition.

This should conclude the work on the enums in libmsore/mscore.h.
convert enum LayoutMode into enum class
convert enum PlayMode into enum class

and make enum LayoutFlag a ": char" (making it an enum class requires
more work, as it is used for flags)
convert unnamed enum into enum class Pad
convert enum FileError into enum class

but an attempt to get rid of the FILE_ prefix failed miserably whith
some bizarre compiler error message.
convert enum Key into enum class

and to be able to ret rid of the KEY_ prefix, change enum Tpc's members
by adding (back) the prefix TPC_
convert enum MidiType into enum class

more work needed in midi/midiinstrument.{h,cpp}?
change enum ShortcutFlags to ": char"

as it is used for flags, turning into an enum would require much more
work
convert enum ChunkType into enum class

and adjust entire file to MuseScore coding style
whitespace changes