Colour the error, info and warning lines in the Debug Window

[zedwick]

The Debug Window shows all script log lines in monocolour:

Which makes it difficult to spot error messages, so I added colours:

In this PR it also shows a little message before the first log lines show up:

Users can also no longer edit the log lines shown in the Debug Window, but can select and copy the text.

Note: I updated QtQuick and QtQuick.Controls to get some newer features, which lost a lot of implicit styling from QtQuick.controls 1.x. So I have restyled using HifiConstants.colors from stylesUit. The background is a darker gray, and I had to add the scrollbar back in; it is a little different.

[zedwick]

I had a bit of trouble with scrolling, but I think I have it sorted properly now so that removing log lines no longer breaks the built-in automatic scrolling. I kept in some manual scrolling just in-case, but we do it less often than before.

[zedwick]

I have now also added filtering to the Debug Window.

Can now select a script name from the drop down list at the bottom of the window, which will clear the log lines from the text area above and then only show log lines associated with the selected script name.

Script names are added to the drop down as its log messages are received, so the list will start out empty and only allow filtering once the first log line from that particular script has been received by the window.

[ada-tv]

A label next to the control is good, the arrow isn't necessary.