Nuvolasdk

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* Add Nuvola SDK CI Image Issue: tiliado/nuvolasdk11
* Use Nuvola SDK CI image for CI of scripts. Issue: tiliado/nuvolasdk11
* Store built files on CI failure.

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* Sync version with Nuvola Runtime.

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* new-project, convert-project: Fix zero modification times for files copied from a template inside Nuvola ADK.
Issue: tiliado/nuvolasdk10
* check-project: Files with zero modification times are detected. Issue: tiliado/nuvolasdk10

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* Circle CI jobs now use Fedora 29.
* Per-application screenshots are used in AppStream metadata. Issue: tiliado/nuvolasdk5

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* The demo player example was updated with shuffle/repeat functionality.
Issue: tiliado/nuvolaruntime20, tiliado/nuvolaruntime21
* new-project, convert-project: CircleCI configuration was added to run `nuvolasdk check-project` when a new commit
is pushed. Look at [Tiliado projet at CircleCI](https://circleci.com/gh/tiliado) to see the results.
Issue: tiliado/nuvolaruntime420

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* New dependency for building Nuvola scripts: [Pillow](https://pypi.org/project/Pillow/) >= 4.3
* check-project: Added check that `metadata.in.json` use two spaces for indentation and no trailing whitespace.
* convert-project: Save `metadata.in.json` with correct indentation and no trailing whitespace.
* new-project: README.md template was updated.
* convert-project: Create `template--README.md` & `template--README.md.diff` to help with the update of README.md.
* new-project: The `integrate.js` template uses Standard JS code style.
* convert-project: Convert `integrate.js` to Standard JS code style.
* check-project: Check that `integrate.js` uses Standard JS code style.
* convert-project: API number in metadata is upgraded to that of Nuvola SDK.
* Makefile generator: If `src/webview.png` image is found, it is used to generate screenshots combining that web view
snapshot image with base Nuvola screenshots. The resulting images can be found in the screenshots subdirectory.
More screenshot types will be added in the next development cycle. Issue: tiliado/nuvolasdk5