New name: HearthStats Companion!

We've changed the name from HearthStats.net Uploader to HearthStats Companion.

This checkin has all the UI name changes, ready for release in v0.19.0.

Changing the name of the project on GitHub and the name of the output .jar files will come later, because the old updaters will not be able to cope with the new name. We'll need to get everyone on to v0.19.0 or later before we can start changing the project name.