Remove apostrophes in icon macro

Removing apostrophes in twig icon macro, that was actually generating an 'attr.icon' instead of the value in attr.icon variable
Merge pull request #189 from tiagobrito/patch-1

Remove apostrophes in icon macro
tabs can be stacked
Merge pull request #190 from aur1mas/stacked-tabs

stacked-tabs
Fixed bug introduced in #190
Added a method to reset the flash bag
Merge pull request #192 from JulienRamel/develop

Added a method to reset the flash bag
Fixed the coding style
Merge pull request #193 from JulienRamel/develop

Fixed the coding style
Removed appending nav class to list childs

The nav class on children gives weird padding on them (bootstrap 3), should only be used on root level element.
Merge pull request #196 from Opifer/develop

Removed appending nav class to list childs
Added nav class to top level item

Additional fix to 13517151d03eacf74dc995e89e3a7030cba6d2a3
Merge pull request #197 from dylanschoenmakers/patch-1

Added nav class to top level item
Add parse_icons function for prepend and append input group
Merge pull request #198 from yvh/develop

Add parse_icons function for prepend and append input group
Changeable default button classes
Merge pull request #187 from sandello-alkr/patch-1

Type of button can be changed using `attr` array.
Removed class "row" from form-group. Fixes #168
Updated README for 2.0.1 release
Extends the default KnpMenu template