Cpp clangformat

[dsazonoff]

Support for clang-format code formatting and code style verification. Issue: #713
Note that this PR is based on #803
Added 2 new cmake targets:

• clang-format-apply - calls clang-format before building sources (only for non-generated files)
• clang-format-verify - verify that current branch:commit follows google code style (a build step to verify code style of pull requests)

[agones-bot]

Build Failed 😱

Build Id: c7bb3a0d-a521-4d60-be3a-280b322b93a3

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[agones-bot]

Build Failed 😱

Build Id: 96f7f9b1-1eaf-4a1a-8336-2dc3dae67f26

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[agones-bot]

Build Succeeded 👏

Build Id: 6cf316f5-750e-461d-93e6-79e755ff974d

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:0.11.0-6da4b1d
• image: gcr.io/agones-images/agones-sdk:0.11.0-6da4b1d
• image: gcr.io/agones-images/agones-ping:0.11.0-6da4b1d
• Linux C++ SDK (build): agonessdk-0.11.0-6da4b1d-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-0.11.0-6da4b1d.zip

A preview of the website (the last 30 builds are retained):

• https://6da4b1d-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/853/head:pr_853 && git checkout pr_853
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=0.11.0-6da4b1d

[agones-bot]

Build Succeeded 👏

Build Id: a1516f0f-fe23-4cb6-898a-2cd4393c67ee

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:0.11.0-f910114
• image: gcr.io/agones-images/agones-sdk:0.11.0-f910114
• image: gcr.io/agones-images/agones-ping:0.11.0-f910114
• Linux C++ SDK (build): agonessdk-0.11.0-f910114-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-0.11.0-f910114.zip

A preview of the website (the last 30 builds are retained):

• https://f910114-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/853/head:pr_853 && git checkout pr_853
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=0.11.0-f910114

[dsazonoff]

Not ready yet...