Enforce .editorconfig by running eclint (#213)

* tune .editorconfig for the existing files
* fix reported linting issues
* travis: switch language to node_js to be able to run npm
* travis: build on ubuntu bionic

.editorconfig

@@ -5,6 +5,25 @@ root = true
 
 [*]
 charset = utf-8
+indent_style = tab
 end_of_line = lf
 trim_trailing_whitespaces = true
-indent_style = tab
+
+[{*.{yml,yaml},.yamllint}]
+indent_style = space
+indent_size = 2
+
+[*.{md,txt}]
+indent_style = space
+trim_trailing_whitespace = false
+
+[Dockerfile*]
+indent_style = space
+indent_size = 4
+
+[*.py]
+indent_style = space
+indent_size = 4
+
+[*.ldif]
+indent_style = space