Re-organize strings

Add comments, rename some strings, remove unused strings

nextcloud/src/main/java/de/mm20/launcher2/nextcloud/LoginActivity.kt

@@ -29,13 +29,13 @@ class LoginActivity : AppCompatActivity() {
                     url = "https://$url"
                 }
                 if (url.isBlank()) {
-                    binding.serverUrlInputLayout.error = getString(R.string.next_cloud_server_url_empty)
+                    binding.serverUrlInputLayout.error = getString(R.string.nextcloud_server_url_empty)
                     return@launch
                 }
                 if (nextcloudClient.checkNextcloudInstallation(url)) {
                     openLoginPage(url)
                 } else {
-                    binding.serverUrlInputLayout.error = getString(R.string.next_cloud_server_invalid_url)
+                    binding.serverUrlInputLayout.error = getString(R.string.nextcloud_server_invalid_url)
                 }
             }
         }

nextcloud/src/main/res/layout/activity_nextcloud_login.xml

@@ -25,7 +25,7 @@
             android:layout_height="wrap_content"
             android:layout_marginTop="32dp"
             android:layout_marginBottom="32dp"
-            android:hint="@string/next_cloud_server_url"
+            android:hint="@string/nextcloud_server_url"
             app:helperTextEnabled="true">
 
             <com.google.android.material.textfield.TextInputEditText
@@ -40,7 +40,7 @@
             style="@style/Widget.MaterialComponents.Button"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:text="@string/login_flow_next" />
+            android:text="@string/login_flow_continue" />
 
     </LinearLayout>
 </FrameLayout>