Lots of stuff in this commit:
1. Implement [Start/Stop/Restart] and make it not possible for
the GUI to interact with that UI if [Helper] is doing stuff.
This prevents the obviously bad situation where [Helper] is in
the middle of spawning P2Pool, but the user is still allowed to
start it again, which would spawn another P2Pool. The main GUI
matches on the state and disables the appropriate UI so the
user can't do this.
2. Sync P2Pool's [Priv] and [Pub] output so that the GUI thread
is only rendering it once a second. All of Gupax also refreshes
at least once a second now as well.
3. Match the [ProcessState] with some colors in the GUI
4. GUI thread no longer directly starts/stops/restarts a process.
It will call a function in [Helper] that acts as a proxy.
5. The tokio [async_spawn_p2pool_watchdog()] function that was
a clone of the PTY version (but had async stuff) and all of the
related functions like the async STDOUT/STDERR reader is now
completely gone. It doesn't make sense to write the same code
twice, both [Simple] and [Advanced] will have a PTY, only
difference being the [Simple] UI won't have an input box.
6. P2Pool's exit code is now examined, either success or failure
7. Output was moved into it's own [Arc<Mutex>]. This allows for
more efficient writing/reading since before I had to lock all of
[Helper], which caused some noticable deadlocks in the GUI.
8. New [tab] field in [State<Gupax>], and GUI option to select
the tab that Gupax will start on.
