themes: add property CurrentBackground
themes: remove property CurrentBackground, CurrentSoundTheme, update SetBackgroundFile(), SetSoundTheme()
themes: rename SoundThemeName to SoundTheme
Merge branch 'develop' of https://github.com/linuxdeepin/dde-daemon into develop

Conflicts:
	themes/manager.go
	themes/manager_stub.go
Merge branch 'develop' of https://github.com/linuxdeepin/dde-daemon into develop