#153. Post data processing refactoring, some changes in form functional.
#153. Fixed issue with null value, post form refactoring completed.
#153. Statistics slightly refactored.
#153. Added commas into arrays, removed empty lines after function body start
#153. Backmerge with master.
#153. Backmerge with master. Fixed metabox.
#153. Sanitizer fixed.
#153. Minor changes in statistics forms.
#153. Fixed errors on frontend.
#153. Pricing tab category default price setting refactored.
#153. Removed diff parts from comments.
Merge pull request #412 from laterpay/feature/153_validate_user_inputs

Feature/153 validate user inputs
Closes #153