Plugins: provide step indicator during installation

[dcdenu4]

When installing a plugin, it can take quite a bit of time. And though the spinny wheel is a great indicator it can feel like nothing is happening. I wonder if we could add a "M out of N steps completed" progress callback? I think that updating would help reassure users it's working.

[emlys]

The more I work on this, the more it seems like there isn't a great solution... I haven't figured out how to keep the series of commands happening in order, while streaming their output. Unlike the invest model logging, there's a series of commands that must be run sequentially. A step indicator is doable, but of the 5 steps, only 2 take any noticeable amount of time, so it doesn't add a lot of information. The most useful way to check the progress is to tail the log file.