main: use "screen" instead of "monitor" to be consistent
Cleanup and add global includes to widgets.h/wkline.h
Add include guards to wkline.h and widgets.h
waf: update widgets build rule
wkline: refactor wkline struct

Properties from config.json are now stored directly in a config struct
similar to the widgets.
widgets: make wkline config struct available to widgets
widgets/xcb: use screen number from config
widgets/magick: use height from config
Move global macros to wkline.h
widgets/notifications: remove static declaration from header
Move web_view ptr to wkline struct
Remove unnecessary forward declaration
Remove unnecessary includes
Merge branch 'code-cleanup' into develop