feat(.wButton-neg): Created new button CSS rules.
feat(.wButton-neg): Created new button CSS rules.

Created negative version of the generic buttons for the white background
situations.

beregovoy68/WavesGUI,wavesplatform/UpcoinWallet,wavesplatform/WavesGUI,wavesplatform/UpcoinWallet,beregovoy68/WavesGUI,beregovoy68/WavesGUI,wavesplatform/WavesGUI,wavesplatform/WavesGUI,beregovoy68/WavesGUI,wavesplatform/WavesGUI