Git cleanup

This pull request makes the Unity project more git-friendly. I changed .gitignore to ignore Library and some autogenerated solution files. I removed Library, since this keeps the repo cleaner, and Unity will regenerate this itself for fresh clones of the repo. Switched to "Force Text Mode" assets (in Editor Settings) - this helps git merge changes and allows you to inspect diffs for prefab, settings and scene files, which can sometimes be useful.