Changed API path to v2 instead of v2.0

We discussed whether the minor-version is relevant for the API base-path and came to the conclusion, that it's not really needed as breaking API changes need a new major version anyway.
This commit also removes the trailing slash from the URL which is returned by `getBackendUrl`. This is needed as we composed the API routes in our implementation always with a starting slash thus leading to double slashes.

Example of old behaviour:
getBackendUrl() + '/config'
=> example.com/api/v2.0//config

Example of new behaviuor:
getBackendUrl() + '/config'
=> example.com/api/v2/config

public/api/v2/config

@@ -0,0 +1,31 @@
+{
+  "allowAnonymous": true,
+  "authProviders": {
+    "facebook": true,
+    "github": true,
+    "twitter": true,
+    "gitlab": true,
+    "dropbox": true,
+    "ldap": true,
+    "google": true,
+    "saml": true,
+    "oauth2": true,
+    "email": true,
+    "openid": true
+  },
+  "customAuthNames": {
+    "ldap": "FooBar",
+    "oauth2": "Olaf2",
+    "saml": "aufSAMLn.de"
+  },
+  "specialLinks": {
+    "privacy": "test",
+    "termsOfUse": "test",
+    "imprint": "test"
+  },
+  "version": {
+    "version": "mock",
+    "sourceCodeUrl": "https://www.youtube.com/watch?v=dQw4w9WgXcQ",
+    "issueTrackerUrl": "https://www.youtube.com/watch?v=dQw4w9WgXcQ"
+  }
+}