feat(module:modal): support disable the esc key to close

[hsuanxyz]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #285

What is the new behavior?

When the [nzMaskClosable] or maskClosable is false, disable the esc key

Does this PR introduce a breaking change?

[ ] Yes
[X] No

Other information

考虑到实际使用场景，通过 maskClosable 同时控制蒙层及esc的行为，就像 ant-react 和 material-angular 一样。

[coveralls]

Coverage decreased (-0.03%) to 43.287% when pulling edf8e68 on HsuanXyz:feature-modal-esc into 35112e8 on NG-ZORRO:master.