Added "Error" priority level and optional TAG pass-through and Demo Application

[alberthynek]

Errors can now be displayed on-screen in a different color. Error color can be set the same way regular text color is set, and defaults to red. When logged as an error, LogCat is invoked with .e rather than .i

Logging can pass your own tag through to LogCat (defaults to previous behaviour)

Also includes new demo application - allows for setting of galgo options and seeing the result - as well as providing a sample codebase

[alberthynek]

Hi. I notice our repos have diverged a bit since this was forked - i this a pull request you'd like to see accepted? If so, I can get it up to date.

[hboregio]

Hey @alberthynek, yeah, there were a few other PRs merged into master since you forked it, so your version might be a bit outdated. If you could update your changes so that it's on top of the current code in master, that would be much easier to review. Thanks!

[alberthynek]

Hey @quiqueqs - It should be good to go now (apologies for the number of commits that took)

[hboregio]

Thanks @alberthynek - I'll take a look at it during next week.