"Mark All As Read" not always available

[r10s]

the sidebar introduced a new function "Mark All As Read", which, however, is unexpectedly not available when a chat is muted - but esp. then you want this function as one cares less about a chat anyways :)

same for muted archived chats, which also should count into "All"

the reason for the issue be that jsonrpc-pendents of dc_get_fresh_msg_cnt()/dc_get_fresh_msgs() are used to show/hide the option and to mark chats as read - however, already by its name "fresh" is not "all" :)

if these information are not easily available in the UI, we should consider adding dedicated core functions as dc_has_unnoticed_chats() and dc_marknoticed_all_chats() (due to multiple meanings, we avoid the the term "read" in the api, cmp)

no "Mark All As Read" here although there are unread chats