Prompt partially supported; each cmd process spawned own process. #1

The CmdProcess.java class now sends a prompt when the current command finishes
executing. The CmdTabPane.java class now intelligent enough to place all output
text before the prompt, although this support in incomplete.

Also, commands are now dispatched into their own Process, rather than reusing
the same process for all commands. This allows use of Process.waitFor() so we
can tell when a command has finished executing.

TODO
With the Process changes, there might be no need to rely on cmd.exe.
CmdProcess.java can parse and dispatch commands itself, rather than relying on
cmd.exe for that functionality. However, some commands, such as echo and dir,
will need to be custom-written if they are cmd.exe commands rather than system
executables. (In other words, if echo and dir are functions performed by
cmd.exe, then CmdProcess will need to implement those functions if we move away
from cmd.exe.)