Added keyboard shortcuts
Enhancement : Shortcuts for onion kin + layer prev

Added 2 new icons :
- Animated Preview Panel : toggle onion skin
- Layers Toolbox : toggle layer preview

Added an icon font generated with icomoon.

SVGs for both icons have been made under Inkscape and are kept under
misc/svg.

All reference SVGs have been moved to misc/svg.

Added 2 keyboard shortcuts for toggling onion skin / layer preview :
- alt L : toggle layer preview
- alt O : toggle onion skin
Fixed layout on FF, removed options in drawer
Fixed input range style on IE11
Add fonts to copy task
Updated font-icon with a better grid
Enhancement : modifiers for Mirror pen
Merge pull request #199 from juliandescottes/enhancement-overlay-shortcut

Enhancement overlay shortcut
Merge pull request #200 from juliandescottes/enhancement-horizontal-mirror

Enhancement : modifiers for Mirror pen
Merge branch 'master' into feature-export-to-file
cleanup of import tab