proper env modifiers support

This implements proper modifier support in the env file using this new fork of the godotenv library. The modifier implementation is quite basic for but can be improved later if needed. See this commit for the actual implementation.

Because we are now using proper modifer parsing, it does not affect the parsing of value, so this is possible again:
```
MY_VAR="#foo"
```
Closes coop-cloud/organising#535

pkg/config/app.go

@@ -25,6 +25,9 @@ import (
 // AppEnv is a map of the values in an apps env config
 type AppEnv = map[string]string
 
+// AppModifiers is a map of modifiers in an apps env config
+type AppModifiers = map[string]map[string]string
+
 // AppName is AppName
 type AppName = string
 
@@ -150,7 +153,7 @@ func (a ByName) Less(i, j int) bool {
 }
 
 func ReadAppEnvFile(appFile AppFile, name AppName) (App, error) {
-	env, err := ReadEnv(appFile.Path, ReadEnvOptions{})
+	env, err := ReadEnv(appFile.Path)
 	if err != nil {
 		return App{}, fmt.Errorf("env file for %s couldn't be read: %s", name, err.Error())
 	}