Test for yielding resources
terminal_mux: Add 'j' and 'k' keybindings
terminal_mux.run: LOG output of terminal_log

This patch tweaks the route of 'terminal_log' such that a LOG session
request of this program is directed to the parent rather to itself.
cli_monitor: Resource-balancing support

This patch introduces new commands for dynamically balancing RAM between
subsystems. The 'status' command prints a table with the RAM status of
each subsystem. The 'ram' command changes the quota or a quota limit of
a given subsystem. The quota limit can be defined to allow the on-demand
expansion of the quota. Finally, the 'yield' command can be used to
instruct a subsystem to yield a specified amount of resources.

For trying out the new commands, a so-called 'ram_eater' example has
been added to the 'terminal_mux.run' scenario. This program simulates a
subsystem with a growing demand for resources, yet with the capability
to yield resources when instructed by the parent (i.e., cli_monitor).

Besides implementing the new features, the patch splits the
implementation of 'cli_monitor' into multiple files.