Clean up .gitignore.

Which ones do you guys think we actually need to keep? I always do out of tree builds, so it turns out, I never need any of these.

Note, you can use a .gitconfig entry to specific a local ignore file for things that are consistent across your machine, like *.swp for vi or ~* for emacs.
We need this one for shadow builds in Qt Creator, this is configured via: "Tools" -> "Options" -> "Build & Run" -> "General" -> "Default Build Directory" and the default, I __think__, is: "../build-%{CurrentProject:Name}-%{CurrentKit:FileSystemName}-%{CurrentBuild:Name}"

The project file is currently src.pro so "%{CurrentProject:Name}" is "src" and this configuration detail will be stored in the companion src.pro.user file.  In the future I have proposed that we may change this to be mudlet.pro

I think it would cover the maximum amount of bases if we modified this .gitignore line to be "-build-*/*"