Feature/allow widgets selfclose

[aarranz]

Proposed changes

Allow volatile widgets to self close. This is done by adding a close method on the MashupPlatform.widget API. This PR also adds support for knowing if the widget is running in volatile mode (required to be able to call the close method)

Types of changes

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• [x] I have read the CONTRIBUTING doc
• [ ] I have signed the CLA
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] I have added necessary documentation (if appropriate)
• [x] Any dependent changes have been merged and published in downstream modules

[coveralls]

Coverage increased (+0.006%) to 88.475% when pulling ccf54f7b451a84e2c70b029105fc298b4ac40b79 on aarranz:feature/allow-widgets-selfclose into 87d1bcb16c67c721938ff4fa6cb8491451a9cd41 on Wirecloud:develop.