style: improve design and add logo

- show data icons in thumbnails in data list items
- add app logo
- fix various visibility issues

src/app/modules/data/elements/offers-detail.html

@@ -3,7 +3,7 @@
   <ion-card-content>
     <div *ngFor="let offer of offers">
       <p *ngIf="offer.inPlace">
-        <ion-icon name="pin"></ion-icon>
+        <ion-icon name="location"></ion-icon>
         <a [routerLink]="['/data-detail', offer.inPlace.uid]">{{offer.inPlace.name}}</a>,&nbsp;
         <span *ngIf="offer.availabilityStarts">
           <ion-icon name="calendar"></ion-icon> {{offer.availabilityStarts | amDateFormat:'ll'}}

src/app/modules/data/elements/offers-in-list.html

@@ -1,6 +1,6 @@
 <div>
   <h2>{{offers[0].prices.default | currency:'EUR':'symbol':undefined:'de'}}</h2>
   <p *ngIf="offers[0].inPlace">
-    <ion-icon name="pin"></ion-icon> {{offers[0].inPlace.name}} <span *ngIf="offers.length > 1">...</span>
+    <ion-icon name="location"></ion-icon> {{offers[0].inPlace.name}} <span *ngIf="offers.length > 1">...</span>
   </p>
 </div>