Hotkeys widget; widgets' refactoring; Xresources theme initial support.

 - changed raster separators to vector ones;
 - added terminal colorscheme support (and reading it from .Xresources);
 - refactored widget configs, slight fixes on some widgets;
 - fixes/updates appearance themes;
 - added keyboard widget (to show currently set hotkeys);
 - added spotify backend to the music widget;
 - added possibility to resize floating clients;
 - added screenshots to readme.