app: updates for ESLint 0.9.1 compatibility

New rules were added in that version which showed some stylistic
problems in our code. These code changes are also compatible with
ESLint 0.8.2, which was the version we used before.
Merge pull request #128 from mgeisler/eslint-0.9.1-updates

app: updates for ESLint 0.9.1 compatibility