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.