Pass PHP script as argument

[dantleech]

This PR implements managed processes and features supporting that:

• Channels: replacing hte "eval" pane, this tabbed pane shows output from arbitrary sources, including the "eval" feature.
• Channel content can be "rewound" and played forward with the history.
• Ability to start an arbitrary managed process: debug-tui -- some/process
• stdout/stderr from process is captured and sent to dedicated channels.
• Process can be restarted.

TODO:

• evaluation has been degraded to a "console" output: no "syntax highlighting" or history preservation...
• ...consider preserving output buffers per history entry? or maybe as a diff?
• consider syntax highlighting (for expression evaluations, and maybe context view)
• input lag in some cases - turns out the child process inherited stdin, fixed by detaching stdin.
• show prcess output if process cannot be started on start.
• channels should have limits (e.g. if process outputs MB/GBs of data).
• processes are piled when proces is restarted...

Next

• Support for xdebug notifications (to channels).
• Handle stdin (?)
• Support for setting breakpoints (as this is now more useful, can set breakpoint and restart the process).