Introduce new groupings for check results

[naz]

Objective

Theme fatal errors, errors, warnings, and recommendations should be grouped separately. Eventually, messages should be grouped by (1) message level and then (2) by file.

Grouping design

Fatal errors
Must be fixed to be able to activate theme.

- [file 1]
  - [fatal error 1.1]
  - [fatal error 1.2]
  - …
- [file 2]
  - [fatal error 2.1]
  - [fatal error 2.2]
  - …
- …

Errors
Highly recommended to fix, functionality could be restricted.

- [file 1]
  - [error 1.1]
  - [error 1.2]
  - …
- [file 2]
  - [error 2.1]
  - [error 2.2]
  - …
- …

Warnings

- [file 1]
  - [warning 1.1]
  - [warning 1.2]
  - …
- [file 2]
  - [warning 2.1]
  - [warning 2.2]
  - …
- …

Recommendations

- [file 1]
  - [recommendation 1.1]
  - [recommendation 1.2]
  - …
- [file 2]
  - [recommendation 2.1]
  - [recommendation 2.2]
  - …
- …

Todo:

• [x] fatal error/error grouping
• [ ] investigate skipped group usage
• [ ] add ability to group by file
• [ ] update scoring algorithms based on new grouping
• [ ] update gscan clients to rely on new fatal group (for example displaying them in Ghost admin report)