Feature – Import sorting

[webmaster128]

As noted in #361, we sometimes check-in code with unsorted imports. Right now, this is not detected by the linter/CI and a manual Organize Imports run needs to be done in the IDE. This leads to the problem that the next person who runs an Organize Imports creates a diff in the imports code that is not related to the current work.

In order to avoid this issue, we should have import sorting as part of the default linting process, preferribly with auto-fixing. This gives us:

1. a failing CI in case of unsorted imports
2. automatic saving when the eslint plugin is setup with autofix on save

The explored options were:

1. eslint's native sort-imports: sorts by imported members, not by module. This causes unnecessary diffs when one symbol was imported before and in a PR additional symbols from the same module are imported (multiple vs. single)
2. eslint-plugin-import: does not support sorting within a group
3. eslint-plugin-simple-import-sort: simple and does what we need

There are now two groups of imports, separated by a newline. The first group is global modules, the second one relative imports.