rename icons in accordance with Icon Naming Specification

See http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html
prefer to use icons from theme, return icon of all the available sizes as fallback
don't use icon size in IconManager, don't update actions' icons

IconManager returns icons that support all available sizes.
So we don't need to set icon size in it and we don't need to update
actions, because they can get pixmap of required size automatically.
Merge pull request #56 from volkov0aa/master

Prefer to use icons from system icon theme
build fixes: build options moved into the beginning of main cmake file;link directories for enca when it's located in non-standard path
main window restore: use save/restore geometry methods instead setGemotery/geometry as the original solution does not work correctly on OS X (and wayland probably); unused MW event handlers commented out
QDirModel replaced by much (and I mean really much) faster QFileSystemModel; fm plugin: fixed #57 Option to show hidden files
fm: useless slot/icon removed
fm: saved file tree sorting
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