static code analysis: introduce automated scans via SonarCloud

This adds Travis and Docker configurations for automated scans,
both for master branch and internal PRs.

External PRs won't be checked due to security concerns
(and Travis limitation related to that) - GH and SonarCloud tokens
are not propagated to those.

An organization and project must be created in SonarCloud for reporting,
as well as a technical GH user with mraa repo commit permission, to set
PR statuses in the "checks" section.

Signed-off-by: Alex Tereschenko <alext.mkrs@gmail.com>

docker-compose.yaml

@@ -31,10 +31,20 @@ services:
         - CXX=${CXX:-clang++-3.8}
         - NODE_VERSION=${NODE_VERSION:-v4.4.7}
         - BUILDARCH=${BUILDARCH}
+        - MRAA_SRC_DIR=${MRAA_SRC_DIR:-/usr/src/app}
     environment:
       - http_proxy
       - https_proxy
       - no_proxy
+      - MRAA_SRC_DIR=/usr/src/app
+      - SONAR_TOKEN
+      - SONAR_ORG
+      - SONAR_PROJ_KEY
+      - TRAVIS_BRANCH
+      - TRAVIS_PULL_REQUEST
+      - TRAVIS_REPO_SLUG
+      - TRAVIS_PULL_REQUEST_SLUG
+      - GITHUB_TOKEN
 
   doc:
     extends: main
@@ -82,3 +92,15 @@ services:
     build:
       args:
         - NODE_VERSION=v5.12.0
+
+  sonar-scan:
+    extends: main
+    build:
+      args:
+        - BUILDSWIG=ON
+        - BUILDSWIGPYTHON=ON
+        - BUILDSWIGNODE=ON
+        - BUILDSWIGJAVA=ON
+        - ONEWIRE=ON
+        - JSONPLAT=ON
+    command: bash -c "$${MRAA_SRC_DIR}/sonar-scan.sh"