Use editor defined in `EDITOR` environment variable instead of `vim`

Some versions ago editor from `EDITOR` environment variable was used. But this were broken in latest versions (#2576). Currently it seems that editor should be already known (`editor_presets.go`) or defined in `config.yml`.

Better to use editor in `EDITOR` environment variable with default preset:
```
func standardTerminalEditorPreset(editor string) *editPreset {
return &editPreset{
editTemplate: editor + " -- {{filename}}",
editAtLineTemplate: editor + " +{{line}} -- {{filename}}",
editAtLineAndWaitTemplate: editor + " +{{line}} -- {{filename}}",
editInTerminal: true,
}
}
```
For example, `EDITOR=mcedit` works great with standard terminal editor preset, including line numbers.