[Fix] WorkspaceFrontendContribution is not binded to FrontendApplication

[DoroNahari]

What it does

Bind WorkspaceFrontendContribution to FrontendApplication.
Today they are not binded and this causes the workspaceFrontendContribution.configure() to not being called.
This make the statusBar color blue (instead of purple) even if workspace is not opened.

How to test

Open Theia in browser.
Open browser dev tools.
In the dev tools, open workspace-frontend-contribution.ts file and put breakpoint inside the configure method.

Before:
configure() isn't being called. the debugger doesn't stop inside configure()
After:
configure() is called. the debugger stop inside configure()

Another way:
Open theia without opened workspace or click File -> Close Workspace
Before:
The status bar is blue instead of purple.
After:
The status bar is purple.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

@DoroNahari the changes work well for me, thank you for taking care of it 👍
Please be sure to update the pull-request to include a sign-of (currently failing) so we can merge.

[DoroNahari]

Please be sure to update the pull-request to include a sign-of (currently failing) so we can merge.

Done. you can merge now. Thank you @vince-fugnitto