Pinning chats, subscriber count

Requires database update when upgrading from 0.24

New Features

Show the number of subscribers in group chats and channels; search results sorted by subscriber count.
Pin chats to the top of the chat list.
Dark/light/system-default UI mode in TinodeWeb.
Option to change font size for messages.
Option to send message on Enter vs send on CTRL-Enter.
Allow to continue messaging while a video/audio call is in progress (same topic only for now).

Full Changelog: https://github.com/tinode/chat/compare/v0.24.7...v0.25.0

Requires database update when upgrading from 0.24

Show the number of subscribers in group chats and channels; search results sorted by subscriber count.
Pin chats to the top of the chat list.
Dark/light/system-default UI mode in TinodeWeb.
Option to change font size for messages.
Option to send message on Enter vs send on CTRL-Enter.
Allow to continue messaging while a video/audio call is in progress (same topic only for now).

Full Changelog: https://github.com/tinode/chat/compare/v0.24.7...v0.25.0