Added per-document indentation settings and indentation auto-detect.

Auto-detect executes automatically when loading files.
Minor code cleanup.
Made auto-detect-indentation feature optional in editor settings.
Improved indentation auto-detection and made it enabled by default.

Also updated the Editor settings layout to better communicate the
slightly changed meanings of some of the options.
Merge branch 'master' of https://github.com/Mezomish/juffed
Merge pull request #59 from cessen/master

Merged Per-document indentation settings