978: remove spring-web

Ticket: planning#978 (closed)

• removed dependency
• added OkHttpClient
• created intermediate client to abstract between logic and HTTP handling
• adjusted and extended tests

core/src/test/java/dev/fitko/fitconnect/core/http/HttpClientTest.java

@@ -52,7 +52,7 @@ public class HttpClientTest {
      * See comments at {@link HttpClient#createRequestBody(Map, Object)} for more information
      */
     @Test
-    public void createRequestBodyWithNoColonsInString() throws IOException {
+    public void createRequestBodyWithNoQuotesInString() throws IOException {
 
         RequestBody requestBody = new HttpClient(true).createRequestBody(Map.of(), "abc");