GDB-9366: Drop-down list in Resource view should not be accessible fr…

…om Context tab

## What
When opening the "Resource" view and clicking on the "inference-select" dropdown, there is an empty option. If a new option is selected, the empty option disappear.

## Why
This can happen if the select does not match any option with the value of "nb-model". [More explanation](https://stackoverflow
.com/questions/12654631/why-does-angularjs-include-an-empty-option-in-select/12654812#12654812).
The problem in our code is that the value of the select is an id of a context type, but during initialization, an instance of the context type is used instead of the id. This causes the select not to match the initial value with a passed option.

## How
Fixed the initial value to be the ID of the context type instead of the instance. Renamed the variable "currentContextType" to "currentContextTypeId" for more clarity regarding the expected value.

src/js/angular/explore/controllers.js

@@ -59,7 +59,7 @@ function ExploreCtrl(
 
     $scope.ContextTypes = ContextTypes;
     $scope.contextTypes = ContextType.getAllType();
-    $scope.currentContextType = ContextTypes.EXPLICIT;
+    $scope.currentContextTypeId = ContextTypes.EXPLICIT.id;
     $scope.roles = [RoleType.SUBJECT, RoleType.PREDICATE, RoleType.OBJECT, RoleType.CONTEXT, RoleType.ALL];
 
     $scope.resourceInfo = undefined;

src/pages/explore.html

@@ -60,8 +60,8 @@ <h1 fit-text fit-text-min="30">
         <label for="inference-select" class="mb-0">
             <select id="inference-select"
                     class="form-control form-control-sm"
-                    ng-model="currentContextType"
-                    ng-change="changeInference(currentContextType)"
+                    ng-model="currentContextTypeId"
+                    ng-change="changeInference(currentContextTypeId)"
                     ng-disabled="loading || resourceInfo.role === 'context' || getActiveRepository() === 'SYSTEM'">
                 <option ng-repeat="contextType in contextTypes"
                         value="{{contextType.id}}"