Added inputMargin to LESS variables
Added button margins

* using @inputMargin
* ajacent buttons have left margin
Hiding inner spins of number inputs
Limiting value setting to min < value < max
Major compatibility fix for Firefox and IE with buttons

Fixed a bug, where buttongroup and -set events were not called properly
with Firefox and IE.
Amend French locales
Add Dutch (The Netherlands, Belgium) locale
Merge pull request #499 from mindtec/Locale_fr_nl

Locale fr nl
Merge pull request #488 from greensolid/develop

Small revision of slider and buttons
merge requests #488, #498