WebXDC improvements, text selection, and more

* WebXDC importFiles and sendToChat
* Optionally allow notifications for replies
* Double-tap to select text, option to quote selection
* Manage channel permissions with a dialog instead of submenu
* Offer to moderate recent messages when banning someone
* Show a large streak of moderated messages as only one
* Fix editing with custom emoji on some platforms
* tel and sms URIs are links
* Expert setting to disable emoji autocomplete
* Preserve filenames more often
* Fix Command UI on tablet view
* Display deleted-media messages the same as un-downloaded ones
* Fix back button from locked thread view
* Better timeouts and tor support for link previews
* A reply with only one emoji and some whitespace is still a reaction
* Re-send presence to MUC when sending custom emoji
* Follow thread of my own sent messages, even when autofollow is disabled