Files related to index page added
add a point of selling functionality
generate opening_time resource and replace POSs opening_time-attribute with relation
add rabl gem and create json-views for POS and opening_time
new functionalities: overview page, market stall adding
shanged some styling
delete opening_times css and js + create class-instance 'weekDayNames'
create product_categories and product_assignments
test
Revert "test"

This reverts commit 524fa61b6645f2e8c0d66c9806cc35b0135975ec.
creating shop_type as model
rename opening_time attributes
delete product_category model
delete shop_type model
add detail_info as detailable
refactor and cleanup

- replace class-methods for weekDay-, productCategory- and
shopTypeNames by constants
- add alias_attributes for accesing attributes in camelCase
- create Detailable- and ActiveRecordExtension-module to include
detail_infos by calling has_detail_infos on model + configs
create market_stalls
make product_assignment polymorphic as assignable
validations
prettyfy & update JSON output