improve styling of filter panel

Adapt width so that the date range fits.
Width of form fields is now 100%.
y-range restrictions are now rendered in one line.

pdb-js/src/styles.scss

@@ -70,3 +70,11 @@ a.external-link:after {
 body .mat-select-panel {
   max-height: 500px;
 }
+
+.mat-form-field {
+  font-family: Arial, sans-serif;
+}
+
+mat-form-field {
+  width: 100%;
+}