feat(action): add a way to reactively set an actionbar item's availab…

[cbourget]

…ility and css class

Please check if the PR fulfills these requirements

• The commit message follows our guidelines:https://github.com/infra-geo-ouverte/igo2/blob/master/.github/CONTRIBUTING.md#git-commit-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What is the current behavior? (You can also link to an open issue here)

• Conditions and css classes on actionbar items are set/updated on demand.

What is the new behavior?

• Actions can now have an availability and ngClass observables that remove the need for on-demand updates. This is much more flexible, easier to user and error proof.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications:

Other information: