make the log output faster, and add colors too

[artoonie]

Closes #831
Closes #830

The issue was that appending to the textarea used string concatenation, which required reading the entire log string and recreating it each time a new log message was added. That made each subsequent GUI run slower, and also explains why we didn't see this in the unit tests: it's only a GUI issue. It also caused the GUI to hang for a short bit of time each time a log message was added.

I replaced the TextArea with a ListView. This makes it trivial to do something that I've wanted for a while: colors for log levels. I can change the foreground or background color. I would appreciate feedback on how this looks:

I also removed the word wrap, since the ListView seems to hiccup if there are changing line widths during fast scrolling. If needed, I can try to overcome this, but I like the way it looks without word wrap.

[yezr]

I love the colors. Side scroll totally works. My only nit is the line spacing. Is it possible to move the lines closer?

[artoonie]

demo.mov

Sounds good. I spruced up the style a little more:

1. Reduced line spacing
2. Decided to go back to word-wrap, but this is an easy change either way. I realize there's important info at the end of the line, and may be better to not force a scroll this has changed after this demo video was made
3. Made the highlight reach across the whole line
4. Added the ability to "select" each row and have that row maintain its log severity color (row = a single log string, which may span multiple lines)
5. Added the ability to copy lines via right click

[tarheel]

The code changes seem pretty uncontroversial. Will let @yezr accept.

[artoonie]

From https://docs.oracle.com/javase/8/javafx/api/javafx/application/Platform.html#runLater-java.lang.Runnable-

NOTE: applications should avoid flooding JavaFX with too many pending Runnables. Otherwise, the application may become unresponsive. Applications are encouraged to batch up multiple operations into fewer runLater calls. Additionally, long-running operations should be done on a background thread where possible, freeing up the JavaFX Application Thread for GUI operations.

That was the cause of the GUI lag that has existed outside of this PR, but wasn't as noticeable until the new GUI's loading bar.

@tarheel there is a small final commit on this PR that fixes it -- it's important to get this right to avoid race conditions where the log output never updates. It's the first and only use of a synchronized block in the codebase. Can you take a quick look at commit 21dc086?