This commit includes theming for the Application Menu plugin. Theming for Application Menu is currently located in the whiskermenu.css configuration file.
I've made two separated versions of the gtk override configuration file (See Extra/override/). This is due to some theming that is targeted for XFCE 4.12 desktops which had a negative affect for 4.14.
Updated the INSTALL.md instructions. Moved the gtk override configuration down as an optional setting.
Themed the tasklist toggle :active state for the 4.14 panelbar.
