vue, bootstrap, scss & storelist rework

closes #191 (closed) and #192 (closed)

What does this MR do?

• adds vue
• adds partials/vue-wrapper.twig template and the $this->view->vueComponent)-method
• adds bootstrap
• adds bootstrap-vue
• adds scss loader
• includes the customized bootstrap theme everywhere (in client/src/core.js), but scoped, so it gets only applied to .bootstrap subelements
• StoreList vue component with filtering
• testing the StoreList pagination (includes testing vue and vue-bootstrap)

Todo

• fix overloaded css classes (bootstrap is now scoped in a .bootstrap class)
• StoreControl.php: filtering the json
• tests

For Nick to do

• check over the webpack config to make sure it works (including test environment)
• add .vue file linting (optional) (we decided to do it after our mega MRs are merged)
• css extracting of compiled scss styles

How confident are you it won't break things if deployed?

mostly

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))