Document model for .editorconfig file

[FrediKats]

As part of other features, we need to manipulate with .editorconfig file - read, parse. create. save. So it's better to create abstraction over .editorconfig file syntax.

What element must be described:

• EditorConfigDocument
• EditorConfigDocumentCategory
• EditorConfigDocumentGroup - synthetic type that we will use for logic structurization. Lines started with ### used for introducing group
• EditorConfigDocumentProperty