Search filter component

[juergenhah]

• added a filter button to open the card
• card with vue-multiselect component
• text input field to search for text (javscript text search)
• available data items are shown and can be selected
• selected items are highlighted on the map
• map extend is fitted to selected items
• reset button to clear selected items
• a layer in the layertree for selected items is added

In order to work following changes had to be made:

• dataset: shops-dannstadt.geojson is renamed to shops-dannstadt.json
• the vue-multiselect package is added in package.json