[fix] Let UIManager handle suspend logic (#5304)
[fix] Let UIManager handle suspend logic (#5304)

See <https://github.com/koreader/koreader/issues/2431#issuecomment-526925910>.

Supersedes <https://github.com/koreader/koreader/pull/5302>.
Frenzie/koreader,poire-z/koreader,mwoz123/koreader,pazos/koreader,koreader/koreader,Frenzie/koreader,Hzj-jie/koreader,mihailim/koreader,koreader/koreader,Markismus/koreader,poire-z/koreader,NiLuJe/koreader,NiLuJe/koreader