Allow mobile devices to open the mention drawer when typing "@"

Closes #227, #171, and #250

See merge request !105

Update master with beta

Closes #216 and #229

See merge request !103

scroll down the current chat view when tab is focused again

See merge request !102

Clean code and separate concerns

See merge request !101

# Conflicts:
#   src/solid-xmpp-chat.js

#216 chat history loss

See merge request !100

bugfix: Fix date separator in french language

See merge request !99

#209 capitalize the separator date in fr lang

See merge request !97

#969 Remove optional chaining into converse.js as well

See merge request !96

#969 Transform optional chaining for older browsers

See merge request !95

#209 date separator format

See merge request !94