Update submodules

Update submodules

* coffee-flask e21678b...9a9446d (28):
  > Add comments
  > Workaround the incompatibility created by Matplotlib 3.3.0
  > Suppress Matplotlib's deprecation warning
  > Add TODO
  > Add doc string
  > Add `type` for flavors and build current consumption dynamically
  > Add new beverage `tea` and make buttons larger
  > Add missing quotes in JS handler for disabling identifier
  > Include constant SQL values directly in queries
  > Update debug message
  > Rename DB field identifiers.status to identifiers.active
  > Add support for multiple identifiers per user
  > Wrap long line and unify upper-casing of SQL keywords
  > Separate counting of coffees and club-mate
  > Remove last coffe pack opened button
  > Add support for another beverages (namely club mate)
  > Change the name of the configuration file
  > Fix column name in UNIQUE index
  > Fix duplicate recording of coffees
  > English fixes
  > Make config-related error message more informative
  > Add last coffee pack button
  > Fix data acquisition for flavor graph.
  > Add TODO
  > Add graphs with total coffee consumption on login screen
  > Fix tag in 'user' template
  > Remove unused function
  > Fix incorrect counting of coffees made during time close to midnight

* terminal/src/buildroot 82779ca806...f98ee51dee (2):
  > overlay: Enable useful munin plugins
  > munin-c: Add iostat plugin and fix memory plugin

* terminal/src/mt-apps 8a4c5fe...b50bf70 (2):
  > mt_server: Use "%s" format string in syslog()
  > Uses letters in test identifiers, not only numbers