tune down in-app emoji selector

[r10s]

the in-app emoji selector is worse than what most modern keyboards offer wrt emoji, eg ...

• modern emoji
• stickers

... are available by many keyboards - but not by our in-app emoji selector.

the last update was several years ago, it seems, we cannot really maintain that effort, even if we based on existing upstream (which does not supported older android ...). also, it seems unnecessary as things are already offered by keyboards - and our limited resources are better spent elsewhere.

to move forward on this issue, get some feedback and to not annoy existing users too much, we could do the following:

1. let pref_system_emoji default to true for new installations (existing installation stay as is for now)
2. move option "Appearance / Use System Emoji" to "Advanced / Use In-App Emoji" with the subtitle "In-app emoji often has less features" (just beside "Use In-App Camera")

then, let's see what happens :)

as a successor, we could check out EmojiCompat and see if that can replace emojify() & co. but that can come later as needed and would require are larger cleanup.

@adbenitez @all or do newer androids with really worser-than-our emoji-picker exist? all i have seen recently on androids was way better, even the default stock-androids in the emulators