Normalizing final new lines (decidim#1744)

* Enfore line ending config inside project

* Ammend all missing final new lines

I used the following script

```bash
for file in $(git grep --cached -Il '' | grep -v /vendor/)
do
  if [ -n "$(tail -c 1 < "$file")" ]
  then
    echo >> "$file"
  fi
done

```

* Add an editorconfig file

To try to minimize diff noise caused by different editors.

Author: deivid-rodriguez

.dockerignore

@@ -2,4 +2,4 @@
 .byebug_history
 pkg/
 .git
-.github
+.github

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true