gitlab-ci: initial version

This change adds gitlab CI support. It tests if latest master of esp-idf-template can be built with the commit of ESP-IDF in question. Currently it's a bit lax because both SDK_PATH and IDF_PATH are defined.
This change also changes components/esp32/lib submodule to point to Github over HTTPS instead of SSH, because CI server might not have its SSH keys uploaded to Github.

.gitlab-ci.yml

@@ -0,0 +1,11 @@
+build_template_app:
+  image: espressif/esp32-ci-env
+
+  variables:
+    SDK_PATH: "$CI_PROJECT_DIR"
+    IDF_PATH: "$CI_PROJECT_DIR"
+
+  script:
+    - git clone https://github.com/espressif/esp-idf-template.git
+    - cd esp-idf-template
+    - make all

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "components/esp32/lib"]
 	path = components/esp32/lib
-	url = ssh://git@github.com:espressif/esp32-wifi-lib.git
+	url = https://github.com/espressif/esp32-wifi-lib.git