Update multimedia/subtitelcomposer-kde4 to 0.6.4 and take maintainership

[tcberner]

Summary

• Update to 0.6.4 (kf5 based)
• Add mpv option
• Remove gstreamer option (required)

• I did a little cmake dance around icu...

[rakuco]

MOVED

9170

The explanation here looks confusing. How about the good old "Renamed to multimedia/subtitlecomposer"?

[tcberner]

Fix up MOVED entry as suggested.

[adridg]

Doesn't apply nicely now, probably due to MOVED being updated in the meantime. But LGETM.

[tcberner]

I think I did not commit this, because like kdesvn it will need kboomarkedit, I think...

[tcberner]

This will be done differently after D12966