Added Info / About Dialog

[grolu]

What this PR does / why we need it:

• Added Info dialog to show Dashboard and Gardener Versions and a list of deployed extensions
• Replaced Copyright Year with 2021

Which issue(s) this PR fixes:
Fixes #452 Fixes #498

Special notes for your reviewer:

Release note:

Moved Dashboard and Gardener version information to a dedicated dialog

Operators with admin role can now view a list of the deployed extensions for the Gardener landscape that the Dashboard is connected to

[petersutter]

have you checked how the extensions would look like as columnar layout or as table?

[grolu]

have you checked how the extensions would look like as columnar layout or as table?

as a first proposal, I restored the expansion panel I already implemented in the last draft. Let's collect some ideas how we can improve. A table certainly is an option, also I like to know if you like the rest of this dialog and also the About Button in the Menu. Last time we also discussed f this dialog should open with a click on the Gardener Logo. WDYT?

[petersutter]

I'd prefer the to open this dialog on the about button. At first look I like it very much, however we should display the version information consistently for both the version information at the top and the extension versions below. Collapsing the extension list by default makes sense, I like it.
Can / should the copyright section at the bottom be configurable / hide-able?

[holgerkoser]

\lgtm