Invenio-assets

* Fixes an issue with attribute access and application context errors.

* Adds support for adding Webpack aliases to theme bundles.

* Uses ``webpack-bundle-tracker`` for the generating the Webpack manifest.
* Disables the vendor chunk grouping in Webpack config. Since now the manifest
exposes entry chunk dependencies, the newly added
``UniqueJinjaManifestLoader`` renders (only once) each chunk.
* Adds a ``WebpackThemeBundle`` which uses the ``APP_THEME`` variable to
determine which bundle will be used.
* Removes support for Flask-Assets and Webassets which was deprecated with
the release of Invenio v3.0.

* Webpack now uses by default in debug/development mode folder-level symlinking
* Enabled source maps for Webpack development builds.
* Patched the ``watchpack`` library to support symlink watching via using
``patch-package``.

- Webpack Live-reload plugin.
- Webpack `templates` alias.
- Webpack fix symlinks issue.

- Turn off webpack warnings