feature: change templates
support
feature: add init file
feature: add class for constants
feature(widgets): change structure and add new

- Basic widget template path - widget/widget_name/widget_sub_name
  Sample: widget/navbar/main
- Add simple widgets templates for navbar, footer and header
feature(widgets): change load data mechanism

- Every widget need have get_data method in Widget class
- Method for get data need be named as get_data + widget key from widget config
Sample: get_data_navbar(), get_data_footer_simple
feature: change assets config